Fix recent regressions, &c.

- fix broken `M421` due to less-than-careful optimization
- add HOME_AFTER_DEACTIVATE define to advanced config so not everyone has to rehome after steppers are deactivated
- misc. cleanups (remove unused label, unused variables)

Marlin/Configuration_adv.h

 #define DEFAULT_MINIMUMFEEDRATE       0.0     // minimum feedrate
 #define DEFAULT_MINTRAVELFEEDRATE     0.0
 
+//#define HOME_AFTER_DEACTIVATE  // Require rehoming after steppers are deactivated
+
 // @section lcd
 
 #if ENABLED(ULTIPANEL)

Marlin/Marlin_main.cpp

 #if HAS_PROBING_PROCEDURE || HOTENDS > 1 || ENABLED(Z_PROBE_ALLEN_KEY) || ENABLED(Z_PROBE_SLED) || ENABLED(NOZZLE_CLEAN_FEATURE) || ENABLED(NOZZLE_PARK_FEATURE) || ENABLED(DELTA_AUTO_CALIBRATION)
 
   bool axis_unhomed_error(const bool x/*=true*/, const bool y/*=true*/, const bool z/*=true*/) {
+#if ENABLED(HOME_AFTER_DEACTIVATE)
     const bool xx = x && !axis_known_position[X_AXIS],
                yy = y && !axis_known_position[Y_AXIS],
                zz = z && !axis_known_position[Z_AXIS];
+#else
+    const bool xx = x && !axis_homed[X_AXIS],
+               yy = y && !axis_homed[Y_AXIS],
+               zz = z && !axis_homed[Z_AXIS];
+#endif
     if (xx || yy || zz) {
       SERIAL_ECHO_START;
       SERIAL_ECHOPGM(MSG_HOME " ");
    */
   inline void gcode_M421() {
     const bool hasX = code_seen('X'), hasI = code_seen('I');
-    const int8_t ix = hasI ? code_value_byte() : hasX ? mbl.probe_index_x(RAW_X_POSITION(code_value_linear_units())) : -1;
+    const int8_t ix = hasI ? code_value_int() : hasX ? mbl.probe_index_x(RAW_X_POSITION(code_value_linear_units())) : -1;
     const bool hasY = code_seen('Y'), hasJ = code_seen('J');
-    const int8_t iy = hasJ ? code_value_byte() : hasY ? mbl.probe_index_y(RAW_Y_POSITION(code_value_linear_units())) : -1;
-    const bool hasZ = code_seen('Z'), hasQ = code_seen('Q');
+    const int8_t iy = hasJ ? code_value_int() : hasY ? mbl.probe_index_y(RAW_Y_POSITION(code_value_linear_units())) : -1;
+    const bool hasZ = code_seen('Z'), hasQ = !hasZ && code_seen('Q');
 
-    if (int(hasI && hasJ) + int(hasX && hasY) != 1 || hasZ == hasQ) {
+    if (int(hasI && hasJ) + int(hasX && hasY) != 1 || !(hasZ || hasQ)) {
       SERIAL_ERROR_START;
       SERIAL_ERRORLNPGM(MSG_ERR_M421_PARAMETERS);
     }
    */
   inline void gcode_M421() {
     const bool hasI = code_seen('I');
-    const int8_t ix = hasI ? code_value_byte() : -1;
+    const int8_t ix = hasI ? code_value_int() : -1;
     const bool hasJ = code_seen('J');
-    const int8_t iy = hasJ ? code_value_byte() : -1;
-    const bool hasZ = code_seen('Z'), hasQ = code_seen('Q');
+    const int8_t iy = hasJ ? code_value_int() : -1;
+    const bool hasZ = code_seen('Z'), hasQ = !hasZ && code_seen('Q');
 
-    if (!hasI || !hasJ || hasZ == hasQ) {
+    if (!hasI || !hasJ || !(hasZ || hasQ)) {
       SERIAL_ERROR_START;
       SERIAL_ERRORLNPGM(MSG_ERR_M421_PARAMETERS);
     }
    *   M421 C Q<offset>
    */
   inline void gcode_M421() {
-    const mesh_index_pair location = find_closest_mesh_point_of_type(REAL, current_position[X_AXIS], current_position[Y_AXIS], USE_NOZZLE_AS_REFERENCE, NULL, false);
-    const bool hasC = code_seen('C'), hasI = code_seen('I');
-    const int8_t ix = hasI ? code_value_byte() : hasC ? location.x_index : -1;
+    const bool hasC = code_seen('C');
+    const bool hasI = code_seen('I');
+    int8_t ix = hasI ? code_value_int() : -1;
     const bool hasJ = code_seen('J');
-    const int8_t iy = hasJ ? code_value_byte() : hasC ? location.y_index : -1;
-    const bool hasZ = code_seen('Z'), hasQ = code_seen('Q');
+    int8_t iy = hasJ ? code_value_int() : -1;
+    const bool hasZ = code_seen('Z'), hasQ = !hasZ && code_seen('Q');
+
+    if (hasC) {
+      const mesh_index_pair location = find_closest_mesh_point_of_type(REAL, current_position[X_AXIS], current_position[Y_AXIS], USE_NOZZLE_AS_REFERENCE, NULL, false);
+      ix = location.x_index;
+      iy = location.y_index;
+    }
 
-    if (int(hasC) + int(hasI && hasJ) != 1 || hasZ == hasQ) {
+    if (int(hasC) + int(hasI && hasJ) != 1 || !(hasZ || hasQ)) {
       SERIAL_ERROR_START;
       SERIAL_ERRORLNPGM(MSG_ERR_M421_PARAMETERS);
     }

Marlin/configuration_store.cpp

     if (!eeprom_error) {
       const int eeprom_size = eeprom_index;
 
-      const uint16_t tcrc = working_crc;
+      const uint16_t final_crc = working_crc;
 
       // Write the EEPROM header
       eeprom_index = EEPROM_OFFSET;
 
       EEPROM_WRITE(version);
-      EEPROM_WRITE(tcrc);
+      EEPROM_WRITE(final_crc);
 
       // Report storage size
       SERIAL_ECHO_START;
       SERIAL_ECHOPAIR("Settings Stored (", eeprom_size - (EEPROM_OFFSET));
-      SERIAL_ECHOPAIR(" bytes; crc ", tcrc);
+      SERIAL_ECHOPAIR(" bytes; crc ", final_crc);
       SERIAL_ECHOLNPGM(")");
     }
 
 
         // Write crc to MAT along with other data, or just tack on to the beginning or end
 
-        SERIAL_PROTOCOLPAIR("Mesh saved in slot ", slot);
+        SERIAL_PROTOCOLLNPAIR("Mesh saved in slot ", slot);
 
       #else
 
 
         // Compare crc with crc from MAT, or read from end
 
-        SERIAL_PROTOCOLPAIR("Mesh loaded from slot ", slot);
+        SERIAL_PROTOCOLLNPAIR("Mesh loaded from slot ", slot);
 
       #else
 

Marlin/example_configurations/Cartesio/Configuration_adv.h

 #define DEFAULT_MINIMUMFEEDRATE       0.0     // minimum feedrate
 #define DEFAULT_MINTRAVELFEEDRATE     0.0
 
+//#define HOME_AFTER_DEACTIVATE  // Require rehoming after steppers are deactivated
+
 // @section lcd
 
 #if ENABLED(ULTIPANEL)

Marlin/example_configurations/Felix/Configuration_adv.h

 #define DEFAULT_MINIMUMFEEDRATE       0.0     // minimum feedrate
 #define DEFAULT_MINTRAVELFEEDRATE     0.0
 
+//#define HOME_AFTER_DEACTIVATE  // Require rehoming after steppers are deactivated
+
 // @section lcd
 
 #if ENABLED(ULTIPANEL)

Marlin/example_configurations/FolgerTech-i3-2020/Configuration_adv.h

 #define DEFAULT_MINIMUMFEEDRATE       0.0     // minimum feedrate
 #define DEFAULT_MINTRAVELFEEDRATE     0.0
 
+//#define HOME_AFTER_DEACTIVATE  // Require rehoming after steppers are deactivated
+
 // @section lcd
 
 #if ENABLED(ULTIPANEL)

Marlin/example_configurations/Hephestos/Configuration_adv.h

 #define DEFAULT_MINIMUMFEEDRATE       0.0     // minimum feedrate
 #define DEFAULT_MINTRAVELFEEDRATE     0.0
 
+//#define HOME_AFTER_DEACTIVATE  // Require rehoming after steppers are deactivated
+
 // @section lcd
 
 #if ENABLED(ULTIPANEL)

Marlin/example_configurations/Hephestos_2/Configuration_adv.h

 #define DEFAULT_MINIMUMFEEDRATE       0.0     // minimum feedrate
 #define DEFAULT_MINTRAVELFEEDRATE     0.0
 
+//#define HOME_AFTER_DEACTIVATE  // Require rehoming after steppers are deactivated
+
 // @section lcd
 
 #if ENABLED(ULTIPANEL)

Marlin/example_configurations/K8200/Configuration_adv.h

 #define DEFAULT_MINIMUMFEEDRATE       0.0     // minimum feedrate
 #define DEFAULT_MINTRAVELFEEDRATE     0.0
 
+//#define HOME_AFTER_DEACTIVATE  // Require rehoming after steppers are deactivated
+
 // @section lcd
 
 #if ENABLED(ULTIPANEL)

Marlin/example_configurations/K8400/Configuration_adv.h

 #define DEFAULT_MINIMUMFEEDRATE       0.0     // minimum feedrate
 #define DEFAULT_MINTRAVELFEEDRATE     0.0
 
+//#define HOME_AFTER_DEACTIVATE  // Require rehoming after steppers are deactivated
+
 // @section lcd
 
 #if ENABLED(ULTIPANEL)

Marlin/example_configurations/RigidBot/Configuration_adv.h

 #define DEFAULT_MINIMUMFEEDRATE       0.0     // minimum feedrate
 #define DEFAULT_MINTRAVELFEEDRATE     0.0
 
+//#define HOME_AFTER_DEACTIVATE  // Require rehoming after steppers are deactivated
+
 // @section lcd
 
 #if ENABLED(ULTIPANEL)

Marlin/example_configurations/SCARA/Configuration_adv.h

 #define DEFAULT_MINIMUMFEEDRATE       0.0     // minimum feedrate
 #define DEFAULT_MINTRAVELFEEDRATE     0.0
 
+//#define HOME_AFTER_DEACTIVATE  // Require rehoming after steppers are deactivated
+
 // @section lcd
 
 #if ENABLED(ULTIPANEL)

Marlin/example_configurations/TAZ4/Configuration_adv.h

 #define DEFAULT_MINIMUMFEEDRATE       0.0     // minimum feedrate
 #define DEFAULT_MINTRAVELFEEDRATE     0.0
 
+//#define HOME_AFTER_DEACTIVATE  // Require rehoming after steppers are deactivated
+
 // @section lcd
 
 #if ENABLED(ULTIPANEL)

Marlin/example_configurations/TinyBoy2/Configuration_adv.h

 #define DEFAULT_MINIMUMFEEDRATE       0.0     // minimum feedrate
 #define DEFAULT_MINTRAVELFEEDRATE     0.0
 
+//#define HOME_AFTER_DEACTIVATE  // Require rehoming after steppers are deactivated
+
 // @section lcd
 
 #if ENABLED(ULTIPANEL)

Marlin/example_configurations/WITBOX/Configuration_adv.h

 #define DEFAULT_MINIMUMFEEDRATE       0.0     // minimum feedrate
 #define DEFAULT_MINTRAVELFEEDRATE     0.0
 
+//#define HOME_AFTER_DEACTIVATE  // Require rehoming after steppers are deactivated
+
 // @section lcd
 
 #if ENABLED(ULTIPANEL)

Marlin/example_configurations/delta/FLSUN/auto_calibrate/Configuration_adv.h

 #define DEFAULT_MINIMUMFEEDRATE       0.0     // minimum feedrate
 #define DEFAULT_MINTRAVELFEEDRATE     0.0
 
+//#define HOME_AFTER_DEACTIVATE  // Require rehoming after steppers are deactivated
+
 // @section lcd
 
 #if ENABLED(ULTIPANEL)

Marlin/example_configurations/delta/FLSUN/kossel_mini/Configuration_adv.h

 #define DEFAULT_MINIMUMFEEDRATE       0.0     // minimum feedrate
 #define DEFAULT_MINTRAVELFEEDRATE     0.0
 
+//#define HOME_AFTER_DEACTIVATE  // Require rehoming after steppers are deactivated
+
 // @section lcd
 
 #if ENABLED(ULTIPANEL)

Marlin/example_configurations/delta/generic/Configuration_adv.h

 #define DEFAULT_MINIMUMFEEDRATE       0.0     // minimum feedrate
 #define DEFAULT_MINTRAVELFEEDRATE     0.0
 
+//#define HOME_AFTER_DEACTIVATE  // Require rehoming after steppers are deactivated
+
 // @section lcd
 
 #if ENABLED(ULTIPANEL)

Marlin/example_configurations/delta/kossel_mini/Configuration_adv.h

 #define DEFAULT_MINIMUMFEEDRATE       0.0     // minimum feedrate
 #define DEFAULT_MINTRAVELFEEDRATE     0.0
 
+//#define HOME_AFTER_DEACTIVATE  // Require rehoming after steppers are deactivated
+
 // @section lcd
 
 #if ENABLED(ULTIPANEL)

Marlin/example_configurations/delta/kossel_pro/Configuration_adv.h

 #define DEFAULT_MINIMUMFEEDRATE       0.0     // minimum feedrate
 #define DEFAULT_MINTRAVELFEEDRATE     0.0
 
+//#define HOME_AFTER_DEACTIVATE  // Require rehoming after steppers are deactivated
+
 // @section lcd
 
 #if ENABLED(ULTIPANEL)

Marlin/example_configurations/delta/kossel_xl/Configuration_adv.h

 #define DEFAULT_MINIMUMFEEDRATE       0.0     // minimum feedrate
 #define DEFAULT_MINTRAVELFEEDRATE     0.0
 
+//#define HOME_AFTER_DEACTIVATE  // Require rehoming after steppers are deactivated
+
 // @section lcd
 
 #if ENABLED(ULTIPANEL)

Marlin/example_configurations/gCreate_gMax1.5+/Configuration_adv.h

 #define DEFAULT_MINIMUMFEEDRATE       0.0     // minimum feedrate
 #define DEFAULT_MINTRAVELFEEDRATE     0.0
 
+//#define HOME_AFTER_DEACTIVATE  // Require rehoming after steppers are deactivated
+
 // @section lcd
 
 #if ENABLED(ULTIPANEL)

Marlin/example_configurations/makibox/Configuration_adv.h

 #define DEFAULT_MINIMUMFEEDRATE       0.0     // minimum feedrate
 #define DEFAULT_MINTRAVELFEEDRATE     0.0
 
+//#define HOME_AFTER_DEACTIVATE  // Require rehoming after steppers are deactivated
+
 // @section lcd
 
 #if ENABLED(ULTIPANEL)

Marlin/example_configurations/tvrrug/Round2/Configuration_adv.h

 #define DEFAULT_MINIMUMFEEDRATE       0.0     // minimum feedrate
 #define DEFAULT_MINTRAVELFEEDRATE     0.0
 
+//#define HOME_AFTER_DEACTIVATE  // Require rehoming after steppers are deactivated
+
 // @section lcd
 
 #if ENABLED(ULTIPANEL)

Marlin/example_configurations/wt150/Configuration_adv.h

 #define DEFAULT_MINIMUMFEEDRATE       0.0     // minimum feedrate
 #define DEFAULT_MINTRAVELFEEDRATE     0.0
 
+//#define HOME_AFTER_DEACTIVATE  // Require rehoming after steppers are deactivated
+
 // @section lcd
 
 #if ENABLED(ULTIPANEL)

Marlin/ubl_G29.cpp

   static int g29_verbose_level, phase_value, repetition_cnt,
              storage_slot = 0, map_type, grid_size;
   static bool repeat_flag, c_flag, x_flag, y_flag;
-  static float x_pos, y_pos, measured_z, card_thickness = 0.0, ubl_constant = 0.0;
+  static float x_pos, y_pos, card_thickness = 0.0, ubl_constant = 0.0;
 
   extern void lcd_setstatus(const char* message, const bool persist);
   extern void lcd_setstatuspgm(const char* message, const uint8_t level);
 
     if (do_ubl_mesh_map) ubl.display_map(map_type);
 
-    LEAVE:
     ubl.restore_ubl_active_state_and_leave();
     KEEPALIVE_STATE(IN_HANDLER);
     do_blocking_move_to_z(Z_CLEARANCE_DEPLOY_PROBE);

Marlin/ultralcd.cpp

      * UBL Build Mesh submenu
      */
     void _lcd_ubl_build_mesh() {
-      int GRID_NUM_POINTS = GRID_MAX_POINTS;
       START_MENU();
       MENU_BACK(MSG_UBL_TOOLS);
       #if (WATCH_THE_BED)