### 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)

Atom target = targets[i];
					Atom &property = targets[i + 1];
					property = _process_selection_request_target(target, p_event->requestor, property, p_event->selection);
				}
				XChangeProperty(x11_display,
						p_event->requestor,
						p_event->property,
						atom_pair,
						32,
						PropModeReplace,
						(unsigned char *)targets,
						len);
				respond.xselection.property = p_event->property;
			}
			XFree(data);
		}
	} else {
		
		respond.xselection.property = _process_selection_request_target(p_event->target, p_event->requestor, p_event->property, p_event->selection);
	}
	respond.xselection.type = SelectionNotify;
	respond.xselection.display = p_event->display;
	respond.xselection.requestor = p_event->requestor;
	respond.xselection.selection = p_event->selection;
	respond.xselection.target = p_event->target;
	respond.xselection.time = p_event->time;
	XSendEvent(x11_display, p_event->requestor, True, NoEventMask, &respond);
	XFlush(x11_display);
}
int DisplayServerX11::_xim_preedit_start_callback(::XIM xim, ::XPointer client_data,