### 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)

ERR_FAIL_COND(!windows.has(p_window));
	const Vector<Vector2> region_path = windows[p_window].mpath;
	int event_base, error_base;
	const Bool ext_okay = XShapeQueryExtension(x11_display, &event_base, &error_base);
	if (ext_okay) {
		if (windows[p_window].mpass) {
			Region region = XCreateRegion();
			XShapeCombineRegion(x11_display, windows[p_window].x11_window, ShapeInput, 0, 0, region, ShapeSet);
			XDestroyRegion(region);
		} else if (region_path.size() == 0) {
			XShapeCombineMask(x11_display, windows[p_window].x11_window, ShapeInput, 0, 0, None, ShapeSet);
		} else {
			XPoint *points = (XPoint *)memalloc(sizeof(XPoint) * region_path.size());
			for (int i = 0; i < region_path.size(); i++) {
				points[i].x = region_path[i].x;
				points[i].y = region_path[i].y;
			}
			Region region = XPolygonRegion(points, region_path.size(), EvenOddRule);
			memfree(points);
			XShapeCombineRegion(x11_display, windows[p_window].x11_window, ShapeInput, 0, 0, region, ShapeSet);
			XDestroyRegion(region);
		}
	}
}
void DisplayServerX11::window_set_rect_changed_callback(const Callable &p_callable, WindowID p_window) {