M600: Fix bug where fan is not turned off

The firmware saves the current fanspeed before parking,
and the fanspeed is restored after unparking. The problem is the fan
was never actually paused.

Fixes #3670

Firmware/Marlin_main.cpp

@@ -3538,6 +3538,9 @@ static void gcode_M600(bool automatic, float x_position, float y_position, float
 
     memcpy(lastpos, current_position, sizeof(lastpos));
 
+    // Turn off the fan
+    fanSpeed = 0;
+
     // Retract E
     current_position[E_AXIS] += e_shift;
     plan_buffer_line_curposXYZE(FILAMENTCHANGE_RFEED);