Fix TERN typo, EXTRA_PROBING

Co-Authored-By: Matthew Kennedy <mattkenn4545@gmail.com>

Marlin/src/inc/Conditionals_LCD.h

     #define PROBE_TRIGGERED_WHEN_STOWED_TEST 1 // Extra test for Allen Key Probe
   #endif
   #if MULTIPLE_PROBING > 1
-    #if EXTRA_PROBING
+    #if EXTRA_PROBING > 0
       #define TOTAL_PROBING (MULTIPLE_PROBING + EXTRA_PROBING)
     #else
       #define TOTAL_PROBING MULTIPLE_PROBING

Marlin/src/inc/SanityCheck.h

     #error "Probes need Z_AFTER_PROBING >= 0."
   #endif
 
-  #if MULTIPLE_PROBING || EXTRA_PROBING
-    #if !MULTIPLE_PROBING
+  #if MULTIPLE_PROBING > 0 || EXTRA_PROBING > 0
+    #if MULTIPLE_PROBING == 0
       #error "EXTRA_PROBING requires MULTIPLE_PROBING."
     #elif MULTIPLE_PROBING < 2
       #error "MULTIPLE_PROBING must be 2 or more."

Marlin/src/module/probe.cpp

     }
   #endif
 
-  #ifdef EXTRA_PROBING
+  #if EXTRA_PROBING > 0
     float probes[TOTAL_PROBING];
   #endif
 
   #if TOTAL_PROBING > 2
     float probes_z_sum = 0;
     for (
-      #if EXTRA_PROBING
+      #if EXTRA_PROBING > 0
         uint8_t p = 0; p < TOTAL_PROBING; p++
       #else
         uint8_t p = TOTAL_PROBING; p--;
 
       const float z = current_position.z;
 
-      #if EXTRA_PROBING
+      #if EXTRA_PROBING > 0
         // Insert Z measurement into probes[]. Keep it sorted ascending.
         LOOP_LE_N(i, p) {                            // Iterate the saved Zs to insert the new Z
           if (i == p || probes[i] > z) {                              // Last index or new Z is smaller than this Z
 
       #if TOTAL_PROBING > 2
         // Small Z raise after all but the last probe
-        if (TERN(EXTRA_PROBING, p < TOTAL_PROBING - 1, p))
-          do_blocking_move_to_z(z + Z_CLEARANCE_MULTI_PROBE, MMM_TO_MMS(Z_PROBE_SPEED_FAST));
+        if (p
+          #if EXTRA_PROBING > 0
+            < TOTAL_PROBING - 1
+          #endif
+        ) do_blocking_move_to_z(z + Z_CLEARANCE_MULTI_PROBE, MMM_TO_MMS(Z_PROBE_SPEED_FAST));
       #endif
     }
 
   #if TOTAL_PROBING > 2
 
-    #if EXTRA_PROBING
+    #if EXTRA_PROBING > 0
       // Take the center value (or average the two middle values) as the median
       static constexpr int PHALF = (TOTAL_PROBING - 1) / 2;
       const float middle = probes[PHALF],