Prevents MINTEMP / MAXTEMP when no heaters present

This commit checks whether or not HEATER_0 is in use, and if not, skips
the MIN / MAX temperature checks.

Marlin/temperature.cpp

@@ -1525,6 +1525,7 @@ ISR(TIMER0_COMPB_vect) {
     for (int i = 0; i < 4; i++) raw_temp_value[i] = 0;
     raw_temp_bed_value = 0;
 
+	#if HAS_TEMP_0
 		#ifndef HEATER_0_USES_MAX6675
 		  #if HEATER_0_RAW_LO_TEMP > HEATER_0_RAW_HI_TEMP
 			#define GE0 <=
@@ -1534,6 +1535,7 @@ ISR(TIMER0_COMPB_vect) {
 		  if (current_temperature_raw[0] GE0 maxttemp_raw[0]) max_temp_error(0);
 		  if (minttemp_raw[0] GE0 current_temperature_raw[0]) min_temp_error(0);
 		#endif
+	#endif
 
     #if HAS_TEMP_1
       #if HEATER_1_RAW_LO_TEMP > HEATER_1_RAW_HI_TEMP