Fix M303 thermal protection

Marlin/src/module/temperature.cpp

     int cycles = 0;
     bool heating = true;
 
-    millis_t temp_ms = millis(), t1 = temp_ms, t2 = temp_ms;
+    millis_t next_temp_ms = millis(), t1 = next_temp_ms, t2 = next_temp_ms;
     long t_high = 0, t_low = 0;
 
     long bias, d;
     float max = 0, min = 10000;
 
     #if HAS_AUTO_FAN
-      next_auto_fan_check_ms = temp_ms + 2500UL;
+      next_auto_fan_check_ms = next_temp_ms + 2500UL;
     #endif
 
     if (hotend >=
     // PID Tuning loop
     while (wait_for_heatup) {
 
-      millis_t ms = millis();
+      const millis_t ms = millis();
 
       if (temp_meas_ready) { // temp sample ready
         updateTemperaturesFromRawValues();
       #define MAX_OVERSHOOT_PID_AUTOTUNE 20
       if (input > temp + MAX_OVERSHOOT_PID_AUTOTUNE) {
         SERIAL_PROTOCOLLNPGM(MSG_PID_TEMP_TOO_HIGH);
-        return;
+        break;
       }
       // Every 2 seconds...
-      if (ELAPSED(ms, temp_ms + 2000UL)) {
+      if (ELAPSED(ms, next_temp_ms)) {
         #if HAS_TEMP_HOTEND || HAS_TEMP_BED
           print_heaterstates();
           SERIAL_EOL();
         #endif
 
-        temp_ms = ms;
+        next_temp_ms = ms + 2000UL;
       } // every 2 seconds
-      // Over 2 minutes?
-      if (((ms - t1) + (ms - t2)) > (10L * 60L * 1000L * 2L)) {
+      // Timeout after 20 minutes since the last undershoot/overshoot cycle
+      if (((ms - t1) + (ms - t2)) > (20L * 60L * 1000L)) {
         SERIAL_PROTOCOLLNPGM(MSG_PID_TIMEOUT);
-        return;
+        break;
       }
       if (cycles > ncycles) {
         SERIAL_PROTOCOLLNPGM(MSG_PID_AUTOTUNE_FINISHED);
       }
       lcd_update();
     }
-    if (!wait_for_heatup) disable_all_heaters();
+    disable_all_heaters();
   }
 
 #endif // HAS_PID_HEATING
 
     for (uint8_t e = 0; e < COUNT(temp_dir); e++) {
       const int16_t tdir = temp_dir[e], rawtemp = current_temperature_raw[e] * tdir;
-      if (rawtemp > maxttemp_raw[e] * tdir && target_temperature[e] > 0) max_temp_error(e);
-      if (rawtemp < minttemp_raw[e] * tdir && !is_preheating(e) && target_temperature[e] > 0) {
+      const bool heater_on = 0 <
+        #if ENABLED(PIDTEMP)
+          soft_pwm_amount[e]
+        #else
+          target_temperature[e]
+        #endif
+      ;
+      if (rawtemp > maxttemp_raw[e] * tdir && heater_on) max_temp_error(e);
+      if (rawtemp < minttemp_raw[e] * tdir && !is_preheating(e) && heater_on) {
         #ifdef MAX_CONSECUTIVE_LOW_TEMPERATURE_ERROR_ALLOWED
           if (++consecutive_low_temperature_error[e] >= MAX_CONSECUTIVE_LOW_TEMPERATURE_ERROR_ALLOWED)
         #endif
       #else
         #define GEBED >=
       #endif
-      if (current_temperature_bed_raw GEBED bed_maxttemp_raw && target_temperature_bed > 0) max_temp_error(-1);
-      if (bed_minttemp_raw GEBED current_temperature_bed_raw && target_temperature_bed > 0) min_temp_error(-1);
+      const bool bed_on = 0 <
+        #if ENABLED(PIDTEMPBED)
+          soft_pwm_amount_bed
+        #else
+          target_temperature_bed
+        #endif
+      ;
+      if (current_temperature_bed_raw GEBED bed_maxttemp_raw && bed_on) max_temp_error(-1);
+      if (bed_minttemp_raw GEBED current_temperature_bed_raw && bed_on) min_temp_error(-1);
     #endif
 
   } // temp_count >= OVERSAMPLENR