Disable laser power when PWM goes to 0

Marlin/src/gcode/control/M3-M5.cpp

       const float spindle_laser_power = parser.floatval('S');
       if (spindle_laser_power == 0) {
         WRITE(SPINDLE_LASER_ENABLE_PIN, !SPINDLE_LASER_ENABLE_INVERT);                                    // turn spindle off (active low)
+        analogWrite(SPINDLE_LASER_PWM_PIN, SPINDLE_LASER_PWM_INVERT ? 255 : 0);                           // only write low byte
         delay_for_power_down();
       }
       else {