### Godot version

Godot Engine v4.0.stable.official.92bee43ad

### System information

Windows 10

### Issue description

The documentation states that passing ```null``` into the image parameter of ```set_custom_mouse_cursor``` will change it back to the system cursor, however I find that it removes the cursor's image entirely, rather than setting it to the system's cursor.


### Steps to reproduce

```var isimage = false
var theimage = load("res://final.png")

func _on_my_button_pressed():
    if isimage == false:
        Input.set_custom_mouse_cursor(theimage, Input.CURSOR_ARROW, Vector2(16,16))
        isimage = true
        
    else:
        Input.set_custom_mouse_cursor(null)
        isimage = false```

When the button is pressed, the cursor is meant to change to the new cursor. When it has been pressed a second time, it changes back to the default cursor. However, upon pressing it a second time, it simply disappears. The cursor becomes visible again when the cursor exits and re-enters the window.

### Minimal reproduction project

[null mouse.zip](https://github.com/godotengine/godot/files/10901969/null.mouse.zip)

Button1MotionMask |
					Button2MotionMask | Button3MotionMask |
					Button4MotionMask | Button5MotionMask |
					ButtonMotionMask | KeymapStateMask |
					ExposureMask | VisibilityChangeMask |
					StructureNotifyMask |
					SubstructureNotifyMask | SubstructureRedirectMask |
					FocusChangeMask | PropertyChangeMask |
					ColormapChangeMask | OwnerGrabButtonMask |
					im_event_mask;
			XChangeWindowAttributes(x11_display, wd.x11_window, CWEventMask, &new_attr);
			static unsigned char all_mask_data[XIMaskLen(XI_LASTEVENT)] = {};
			all_event_mask.deviceid = XIAllDevices;
			all_event_mask.mask_len = sizeof(all_mask_data);
			all_event_mask.mask = all_mask_data;
			XISetMask(all_event_mask.mask, XI_HierarchyChanged);
#ifdef TOUCH_ENABLED
			if (xi.touch_devices.size()) {
				XISetMask(all_event_mask.mask, XI_TouchBegin);
				XISetMask(all_event_mask.mask, XI_TouchUpdate);
				XISetMask(all_event_mask.mask, XI_TouchEnd);
				XISetMask(all_event_mask.mask, XI_TouchOwnership);
			}
#endif
			XISelectEvents(x11_display, wd.x11_window, &all_event_mask, 1);
		}
		
		XStoreName(x11_display, wd.x11_window, "Godot");
		XSetWMProtocols(x11_display, wd.x11_window, &wm_delete, 1);
		if (xdnd_aware != None) {