### 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)

}
	Ref<InputEventFromWindow> event_from_window = p_event;
	if (event_from_window.is_valid() && event_from_window->get_window_id() != INVALID_WINDOW_ID) {
		
		if (windows.has(event_from_window->get_window_id())) {
			Callable callable = windows[event_from_window->get_window_id()].input_event_callback;
			if (callable.is_valid()) {
				callable.callp((const Variant **)&evp, 1, ret, ce);
			}
		}
	} else {
		
		for (KeyValue<WindowID, WindowData> &E : windows) {
			Callable callable = E.value.input_event_callback;
			if (callable.is_valid()) {
				callable.callp((const Variant **)&evp, 1, ret, ce);
			}
		}
	}
}
void DisplayServerX11::_send_window_event(const WindowData &wd, WindowEvent p_event) {
	if (!wd.event_callback.is_null()) {
		Variant event = int(p_event);
		Variant *eventp = &event;
		Variant ret;
		Callable::CallError ce;
		wd.event_callback.callp((const Variant **)&eventp, 1, ret, ce);
	}
}
void DisplayServerX11::_poll_events_thread(void *ud) {