Merge pull request #3066 from Blue-Marlin/Fix-disable_all_heaters()

Fix disable_all_heaters() for MAX6675

Marlin/temperature.cpp

     WRITE_HEATER_ ## NR (LOW); \
   }
 
-  #if HAS_TEMP_0
+#if HAS_TEMP_0 || ENABLED(HEATER_0_USES_MAX6675)
     target_temperature[0] = 0;
     soft_pwm[0] = 0;
     WRITE_HEATER_0P(LOW); // Should HEATERS_PARALLEL apply here? Then change to DISABLE_HEATER(0)