### 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)

p_target,
				8,
				PropModeReplace,
				(unsigned char *)clip.get_data(),
				clip.length());
		return p_property;
	} else {
		char *target_name = XGetAtomName(x11_display, p_target);
		print_verbose(vformat("Target '%s' not supported.", target_name));
		if (target_name) {
			XFree(target_name);
		}
		return None;
	}
}
void DisplayServerX11::_handle_selection_request_event(XSelectionRequestEvent *p_event) const {
	XEvent respond;
	if (p_event->target == XInternAtom(x11_display, "MULTIPLE", 0)) {
		
		Atom atom_pair = XInternAtom(x11_display, "ATOM_PAIR", False);
		respond.xselection.property = None;
		Atom type;
		int format;
		unsigned long len;
		unsigned long remaining;
		unsigned char *data = nullptr;
		if (XGetWindowProperty(x11_display, p_event->requestor, p_event->property, 0, LONG_MAX, False, atom_pair, &type, &format, &len, &remaining, &data) == Success) {
			if ((len >= 2) && data) {
				Atom *targets = (Atom *)data;
				for (uint64_t i = 0; i < len; i += 2) {