### 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)

}
				wd.focused = false;
				Input::get_singleton()->release_pressed_events();
				_send_window_event(wd, WINDOW_EVENT_FOCUS_OUT);
				if (mouse_mode_grab) {
					for (const KeyValue<WindowID, WindowData> &E : windows) {
						
						if (mouse_mode == MOUSE_MODE_CAPTURED) {
							
							XUndefineCursor(x11_display, E.value.x11_window);
						}
					}
					XUngrabPointer(x11_display, CurrentTime);
				}
#ifdef TOUCH_ENABLED
				
				/*for (int i = 0; i < xi.touch_devices.size(); ++i) {
					XIUngrabDevice(x11_display, xi.touch_devices[i], CurrentTime);
				}*/
				
				for (const KeyValue<int, Vector2> &E : xi.state) {
					Ref<InputEventScreenTouch> st;
					st.instantiate();
					st->set_index(E.key);
					st->set_window_id(window_id);
					st->set_position(E.value);
					Input::get_singleton()->parse_input_event(st);
				}
				xi.state.clear();
#endif