Fixed M109 timer overflow (reported by triffid)

Marlin/Marlin.pde

@@ -842,7 +842,7 @@ void process_commands()
         /* continue to loop until we have reached the target temp   
           _and_ until TEMP_RESIDENCY_TIME hasn't passed since we reached it */
         while((residencyStart == -1) ||
-              (residencyStart > -1 && (millis() - residencyStart) < TEMP_RESIDENCY_TIME*1000) ) {
+              (residencyStart > -1 && (millis() - residencyStart) < TEMP_RESIDENCY_TIME*1000l) ) {
       #else
         while ( target_direction ? (isHeatingHotend(tmp_extruder)) : (isCoolingHotend(tmp_extruder)&&(CooldownNoWait==false)) ) {
       #endif //TEMP_RESIDENCY_TIME