This ifdef is for bed code so should use bed constants for testing.

Without this fix, the code wont compile with extruder but without bed
runaway protection defined.

Marlin/temperature.cpp

@@ -572,7 +572,7 @@ void manage_heater()
 
   #if TEMP_SENSOR_BED != 0
   
-    #ifdef THERMAL_RUNAWAY_PROTECTION_PERIOD && THERMAL_RUNAWAY_PROTECTION_PERIOD > 0
+    #if defined(THERMAL_RUNAWAY_PROTECTION_BED_PERIOD) && THERMAL_RUNAWAY_PROTECTION_BED_PERIOD > 0
       thermal_runaway_protection(&thermal_runaway_bed_state_machine, &thermal_runaway_bed_timer, current_temperature_bed, target_temperature_bed, 9, THERMAL_RUNAWAY_PROTECTION_BED_PERIOD, THERMAL_RUNAWAY_PROTECTION_BED_HYSTERESIS);
     #endif