### 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)

GrabModeAsync, GrabModeAsync, E.value.x11_window, None, CurrentTime);
					}
				}
#ifdef TOUCH_ENABLED
				
				/*for (int i = 0; i < xi.touch_devices.size(); ++i) {
					XIGrabDevice(x11_display, xi.touch_devices[i], x11_window, CurrentTime, None, XIGrabModeAsync, XIGrabModeAsync, False, &xi.touch_event_mask);
				}*/
#endif
				if (!app_focused) {
					if (OS::get_singleton()->get_main_loop()) {
						OS::get_singleton()->get_main_loop()->notification(MainLoop::NOTIFICATION_APPLICATION_FOCUS_IN);
					}
					app_focused = true;
				}
			} break;
			case FocusOut: {
				DEBUG_LOG_X11("[%u] FocusOut window=%lu (%u), mode='%u' \n", frame, event.xfocus.window, window_id, event.xfocus.mode);
				WindowData &wd = windows[window_id];
				if (ime_window_event || (event.xfocus.detail == NotifyInferior)) {
					break;
				}
				if (wd.ime_active) {
					MutexLock mutex_lock(events_mutex);
					XUnsetICFocus(wd.xic);
					XUnmapWindow(x11_display, wd.x11_xim_window);
					wd.ime_active = false;
					im_text = String();
					im_selection = Vector2i();
					OS_Unix::get_singleton()->get_main_loop()->notification(MainLoop::NOTIFICATION_OS_IME_UPDATE);