### 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)

break;
				}
				windows[window_id].fullscreen = _window_fullscreen_check(window_id);
				Main::force_redraw();
			} break;
			case NoExpose: {
				DEBUG_LOG_X11("[%u] NoExpose drawable=%lu (%u) \n", frame, event.xnoexpose.drawable, window_id);
				if (ime_window_event) {
					break;
				}
				windows[window_id].minimized = true;
			} break;
			case VisibilityNotify: {
				DEBUG_LOG_X11("[%u] VisibilityNotify window=%lu (%u), state=%u \n", frame, event.xvisibility.window, window_id, event.xvisibility.state);
				if (ime_window_event) {
					break;
				}
				windows[window_id].minimized = _window_minimize_check(window_id);
			} break;
			case LeaveNotify: {
				DEBUG_LOG_X11("[%u] LeaveNotify window=%lu (%u), mode='%u' \n", frame, event.xcrossing.window, window_id, event.xcrossing.mode);
				if (ime_window_event) {
					break;
				}
				if (!mouse_mode_grab) {
					_send_window_event(windows[window_id], WINDOW_EVENT_MOUSE_EXIT);
				}
			} break;
			case EnterNotify: {
				DEBUG_LOG_X11("[%u] EnterNotify window=%lu (%u), mode='%u' \n", frame, event.xcrossing.window, window_id, event.xcrossing.mode);