Fix thermal runaway timeout

Marlin/temperature.cpp

@@ -1241,12 +1241,12 @@ void Temperature::init() {
         *state = TRStable;
       // While the temperature is stable watch for a bad temperature
       case TRStable:
-        if (temperature < tr_target_temperature[heater_index] - hysteresis_degc && ELAPSED(millis(), *timer))
-          *state = TRRunaway;
-        else {
+        if (temperature >= tr_target_temperature[heater_index] - hysteresis_degc) {
           *timer = millis() + period_seconds * 1000UL;
           break;
         }
+        else if (PENDING(millis(), *timer)) break;
+        *state = TRRunaway;
       case TRRunaway:
         _temp_error(heater_id, PSTR(MSG_T_THERMAL_RUNAWAY), PSTR(MSG_THERMAL_RUNAWAY));
     }