### 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)

borderless = !(reinterpret_cast<Hints *>(data)->decorations);
					}
					if (data) {
						XFree(data);
					}
				}
			}
			return borderless;
		} break;
		case WINDOW_FLAG_ALWAYS_ON_TOP: {
			return wd.on_top;
		} break;
		case WINDOW_FLAG_TRANSPARENT: {
			return wd.layered_window;
		} break;
		case WINDOW_FLAG_NO_FOCUS: {
			return wd.no_focus;
		} break;
		case WINDOW_FLAG_MOUSE_PASSTHROUGH: {
			return wd.mpass;
		} break;
		case WINDOW_FLAG_POPUP: {
			return wd.is_popup;
		} break;
		default: {
		}
	}
	return false;
}
void DisplayServerX11::window_request_attention(WindowID p_window) {