Merge pull request #3398 from thinkyhead/rc_sensor_per_extruder

Catch a TEMP_SENSOR error before a pins issue

Marlin/SanityCheck.h

  * Test Heater, Temp Sensor, and Extruder Pins; Sensor Type must also be set.
  */
 #if EXTRUDERS > 3
-  #if !HAS_HEATER_3
+  #if TEMP_SENSOR_3 == 0
+    #error TEMP_SENSOR_3 is required with 4 EXTRUDERS.
+  #elif !HAS_HEATER_3
     #error HEATER_3_PIN not defined for this board.
   #elif !PIN_EXISTS(TEMP_3)
     #error TEMP_3_PIN not defined for this board.
   #elif !PIN_EXISTS(E3_STEP) || !PIN_EXISTS(E3_DIR) || !PIN_EXISTS(E3_ENABLE)
     #error E3_STEP_PIN, E3_DIR_PIN, or E3_ENABLE_PIN not defined for this board.
-  #elif TEMP_SENSOR_3 == 0
-    #error TEMP_SENSOR_3 is required with 4 EXTRUDERS.
   #endif
 #elif EXTRUDERS > 2
-  #if !HAS_HEATER_2
+  #if TEMP_SENSOR_2 == 0
+    #error TEMP_SENSOR_2 is required with 3 or more EXTRUDERS.
+  #elif !HAS_HEATER_2
     #error HEATER_2_PIN not defined for this board.
   #elif !PIN_EXISTS(TEMP_2)
     #error TEMP_2_PIN not defined for this board.
   #elif !PIN_EXISTS(E2_STEP) || !PIN_EXISTS(E2_DIR) || !PIN_EXISTS(E2_ENABLE)
     #error E2_STEP_PIN, E2_DIR_PIN, or E2_ENABLE_PIN not defined for this board.
-  #elif TEMP_SENSOR_2 == 0
-    #error TEMP_SENSOR_2 is required with 3 or more EXTRUDERS.
   #endif
 #elif EXTRUDERS > 1
-  #if !PIN_EXISTS(TEMP_1)
+  #if TEMP_SENSOR_1 == 0
+    #error TEMP_SENSOR_1 is required with 2 or more EXTRUDERS.
+  #elif !PIN_EXISTS(TEMP_1)
     #error TEMP_1_PIN not defined for this board.
   #elif !PIN_EXISTS(E1_STEP) || !PIN_EXISTS(E1_DIR) || !PIN_EXISTS(E1_ENABLE)
     #error E1_STEP_PIN, E1_DIR_PIN, or E1_ENABLE_PIN not defined for this board.
   #endif
 #endif
 
-#if TEMP_SENSOR_1 == 0
-  #if EXTRUDERS > 1
-    #error TEMP_SENSOR_1 is required with 2 or more EXTRUDERS.
-  #elif ENABLED(TEMP_SENSOR_1_AS_REDUNDANT)
-    #error TEMP_SENSOR_1 is required with TEMP_SENSOR_1_AS_REDUNDANT.
-  #endif
+#if ENABLED(TEMP_SENSOR_1_AS_REDUNDANT) && TEMP_SENSOR_1 == 0
+  #error TEMP_SENSOR_1 is required with TEMP_SENSOR_1_AS_REDUNDANT.
 #endif
 
 #if !HAS_HEATER_0