### 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 (property == None) {
		return retval;
	}
	int result = XGetWindowProperty(
			x11_display,
			wd.x11_window,
			property,
			0,
			1024,
			False,
			XA_ATOM,
			&type,
			&format,
			&len,
			&remaining,
			&data);
	if (result == Success) {
		Atom *atoms = (Atom *)data;
		Atom wm_fullscreen = XInternAtom(x11_display, "_NET_WM_STATE_FULLSCREEN", False);
		for (uint64_t i = 0; i < len; i++) {
			if (atoms[i] == wm_fullscreen) {
				retval = true;
				break;
			}
		}
		XFree(data);
	}
	return retval;
}
void DisplayServerX11::_validate_mode_on_map(WindowID p_window) {