### 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)

if (data) {
						XFree(data);
					}
					if (done) {
						break;
					}
				}
			}
			if (success && (data_size > 0)) {
				ret.parse_utf8((const char *)incr_data.ptr(), data_size);
			}
		} else if (bytes_left > 0) {
			
			result = XGetWindowProperty(x11_display, x11_window,
					selection, 0, bytes_left, 0,
					AnyPropertyType, &type, &format,
					&len, &dummy, &data);
			if (result == Success) {
				ret.parse_utf8((const char *)data);
			} else {
				print_verbose("Failed to get selection data.");
			}
			if (data) {
				XFree(data);
			}
		}
	}
	return ret;
}
String DisplayServerX11::_clipboard_get(Atom p_source, Window x11_window) const {