### 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)

DisplayServerX11 *display_server = static_cast<DisplayServerX11 *>(ud);
	display_server->_poll_events();
}
Bool DisplayServerX11::_predicate_all_events(Display *display, XEvent *event, XPointer arg) {
	
	return True;
}
bool DisplayServerX11::_wait_for_events() const {
	int x11_fd = ConnectionNumber(x11_display);
	fd_set in_fds;
	XFlush(x11_display);
	FD_ZERO(&in_fds);
	FD_SET(x11_fd, &in_fds);
	struct timeval tv;
	tv.tv_usec = 0;
	tv.tv_sec = 1;
	
	int num_ready_fds = select(x11_fd + 1, &in_fds, nullptr, nullptr, &tv);
	if (num_ready_fds > 0) {
		
		return true;
	} else {
		
		if (num_ready_fds < 0) {
			ERR_PRINT("_wait_for_events: select error: " + itos(errno));
		}
		return false;
	}
}
void DisplayServerX11::_poll_events() {