### 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)

MutexLock mutex_lock(events_mutex);
	for (uint32_t event_index = 0; event_index < polled_events.size(); ++event_index) {
		XEvent &event = polled_events[event_index];
		if (XGetEventData(x11_display, &event.xcookie) && event.xcookie.type == GenericEvent && event.xcookie.extension == xi.opcode) {
			XIDeviceEvent *event_data = (XIDeviceEvent *)event.xcookie.data;
			if (event_data->evtype == XI_RawMotion) {
				XFreeEventData(x11_display, &event.xcookie);
				polled_events.remove_at(event_index--);
				continue;
			}
			XFreeEventData(x11_display, &event.xcookie);
			break;
		}
	}
	xi.relative_motion.x = 0;
	xi.relative_motion.y = 0;
}
#ifdef SPEECHD_ENABLED
bool DisplayServerX11::tts_is_speaking() const {