### 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)

} else if (window_get_flag(WINDOW_FLAG_RESIZE_DISABLED, p_window)) {
		
		xsh->flags |= PMinSize | PMaxSize;
		xsh->min_width = wd.size.x;
		xsh->max_width = wd.size.x;
		xsh->min_height = wd.size.y;
		xsh->max_height = wd.size.y;
	} else {
		
		if (wd.min_size != Size2i()) {
			xsh->flags |= PMinSize;
			xsh->min_width = wd.min_size.x;
			xsh->min_height = wd.min_size.y;
		}
		if (wd.max_size != Size2i()) {
			xsh->flags |= PMaxSize;
			xsh->max_width = wd.max_size.x;
			xsh->max_height = wd.max_size.y;
		}
	}
	XSetWMNormalHints(x11_display, wd.x11_window, xsh);
	XFree(xsh);
}
Point2i DisplayServerX11::window_get_position(WindowID p_window) const {
	_THREAD_SAFE_METHOD_
	ERR_FAIL_COND_V(!windows.has(p_window), Point2i());
	const WindowData &wd = windows[p_window];
	return wd.position;
}
Point2i DisplayServerX11::window_get_position_with_decorations(WindowID p_window) const {