### 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)

_THREAD_SAFE_METHOD_
	ERR_FAIL_COND(!windows.has(p_window));
	WindowData &wd = windows[p_window];
	wd.drop_files_callback = p_callable;
}
int DisplayServerX11::window_get_current_screen(WindowID p_window) const {
	_THREAD_SAFE_METHOD_
	int count = get_screen_count();
	if (count < 2) {
		
		return 0;
	}
	ERR_FAIL_COND_V(!windows.has(p_window), 0);
	const WindowData &wd = windows[p_window];
	const Rect2i window_rect(wd.position, wd.size);
	
	int screen_index = 0;
	int max_area = 0;
	for (int i = 0; i < count; i++) {
		Rect2i screen_rect = _screen_get_rect(i);
		Rect2i intersection = screen_rect.intersection(window_rect);
		int area = intersection.get_area();
		if (area > max_area) {
			max_area = area;
			screen_index = i;
		}
	}
	return screen_index;
}
void DisplayServerX11::gl_window_make_current(DisplayServer::WindowID p_window_id) {