### 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_
	return _screen_get_rect(p_screen).size;
}
int default_window_error_handler(Display *display, XErrorEvent *error) {
	static char message[1024];
	XGetErrorText(display, error->error_code, message, sizeof(message));
	ERR_PRINT(vformat("Unhandled XServer error: %s"
					  "\n   Major opcode of failed request: %d"
					  "\n   Serial number of failed request: %d"
					  "\n   Current serial number in output stream: %d",
			String::utf8(message), (uint64_t)error->request_code, (uint64_t)error->minor_code, (uint64_t)error->serial));
	return 0;
}
bool g_bad_window = false;
int bad_window_error_handler(Display *display, XErrorEvent *error) {
	if (error->error_code == BadWindow) {
		g_bad_window = true;
	} else {
		return default_window_error_handler(display, error);
	}
	return 0;
}
Rect2i DisplayServerX11::screen_get_usable_rect(int p_screen) const {
	_THREAD_SAFE_METHOD_
	p_screen = _get_screen_index(p_screen);
	int screen_count = get_screen_count();
	
	ERR_FAIL_INDEX_V(p_screen, screen_count, Rect2i(0, 0, 0, 0));
	bool is_multiscreen = screen_count > 1;