Merge pull request #1511 from MagoKimbra/Reset_Alert_message_M600

Reset Alert message when finish M600 command

Marlin/Marlin_main.cpp

 
         RUNPLAN; //should do nothing
 
+        //reset LCD alert message
+    	lcd_reset_alert_level();
+
         #ifdef DELTA
           calculate_delta(lastpos);
           plan_buffer_line(delta[X_AXIS], delta[Y_AXIS], delta[Z_AXIS], target[E_AXIS], fr60, active_extruder); //move xyz back