### 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_
	if (!p_text.is_empty()) {
		{
			
			MutexLock mutex_lock(events_mutex);
			internal_clipboard_primary = p_text;
		}
		XSetSelectionOwner(x11_display, XA_PRIMARY, windows[MAIN_WINDOW_ID].x11_window, CurrentTime);
		XSetSelectionOwner(x11_display, XInternAtom(x11_display, "PRIMARY", 0), windows[MAIN_WINDOW_ID].x11_window, CurrentTime);
	}
}
Bool DisplayServerX11::_predicate_clipboard_selection(Display *display, XEvent *event, XPointer arg) {
	if (event->type == SelectionNotify && event->xselection.requestor == *(Window *)arg) {
		return True;
	} else {
		return False;
	}
}
Bool DisplayServerX11::_predicate_clipboard_incr(Display *display, XEvent *event, XPointer arg) {
	if (event->type == PropertyNotify && event->xproperty.state == PropertyNewValue) {
		return True;
	} else {
		return False;
	}
}
String DisplayServerX11::_clipboard_get_impl(Atom p_source, Window x11_window, Atom target) const {