Improve sanitycheck for TEMP_SENSOR_1

Marlin/SanityCheck.h

     #if !HAS_HEATER_2
       #error HEATER_2_PIN not defined for this board.
     #elif TEMP_SENSOR_2 == 0
-      #error TEMP_SENSOR_2 is required with 3 EXTRUDERS.
+      #error TEMP_SENSOR_2 is required with 3 or more EXTRUDERS.
     #endif
   #elif EXTRUDERS > 1 || defined(HEATERS_PARALLEL)
     #if !HAS_HEATER_1
       #error HEATER_1_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
+  #endif
   #if !HAS_HEATER_0
     #error HEATER_0_PIN not defined for this board.
   #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 TEMP_SENSOR_0 == 0
     #error TEMP_SENSOR_0 is required.
   #endif