### 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)

if (event->xany.window == *(Window *)arg) {
		return (event->type == SelectionRequest) ||
				(event->type == SelectionNotify);
	} else {
		return False;
	}
}
void DisplayServerX11::_clipboard_transfer_ownership(Atom p_source, Window x11_window) const {
	_THREAD_SAFE_METHOD_
	Window selection_owner = XGetSelectionOwner(x11_display, p_source);
	if (selection_owner != x11_window) {
		return;
	}
	
	MutexLock mutex_lock(events_mutex);
	Atom clipboard_manager = XInternAtom(x11_display, "CLIPBOARD_MANAGER", False);
	Atom save_targets = XInternAtom(x11_display, "SAVE_TARGETS", False);
	XConvertSelection(x11_display, clipboard_manager, save_targets, None,
			x11_window, CurrentTime);
	
	while (true) {
		if (!_wait_for_events()) {
			
			break;
		}
		
		XEvent ev;