### 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_
	WindowData &wd = windows[MAIN_WINDOW_ID];
	int (*oldHandler)(Display *, XErrorEvent *) = XSetErrorHandler(&set_icon_errorhandler);
	Atom net_wm_icon = XInternAtom(x11_display, "_NET_WM_ICON", False);
	if (p_icon.is_valid()) {
		Ref<Image> img = p_icon->duplicate();
		img->convert(Image::FORMAT_RGBA8);
		while (true) {
			int w = img->get_width();
			int h = img->get_height();
			if (g_set_icon_error) {
				g_set_icon_error = false;
				WARN_PRINT("Icon too large, attempting to resize icon.");
				int new_width, new_height;
				if (w > h) {
					new_width = w / 2;
					new_height = h * new_width / w;
				} else {
					new_height = h / 2;
					new_width = w * new_height / h;
				}
				w = new_width;
				h = new_height;
				if (!w || !h) {
					WARN_PRINT("Unable to set icon.");
					break;
				}
				img->resize(w, h, Image::INTERPOLATE_CUBIC);