### 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)

if (cursor == None) {
			ERR_PRINT("FAILED CREATING CURSOR");
		}
		null_cursor = cursor;
	}
	cursor_set_shape(CURSOR_BUSY);
	
	
	
	XEvent config_event;
	while (XCheckTypedEvent(x11_display, ConfigureNotify, &config_event)) {
		_window_changed(&config_event);
	}
	events_thread.start(_poll_events_thread, this);
	_update_real_mouse_position(windows[MAIN_WINDOW_ID]);
#ifdef DBUS_ENABLED
	screensaver = memnew(FreeDesktopScreenSaver);
	screen_set_keep_on(GLOBAL_GET("display/window/energy_saving/keep_screen_on"));
	portal_desktop = memnew(FreeDesktopPortalDesktop);
#endif
	XSetErrorHandler(&default_window_error_handler);
	r_error = OK;
}
DisplayServerX11::~DisplayServerX11() {
	
	Window x11_main_window = windows[MAIN_WINDOW_ID].x11_window;
	_clipboard_transfer_ownership(XA_PRIMARY, x11_main_window);
	_clipboard_transfer_ownership(XInternAtom(x11_display, "CLIPBOARD", 0), x11_main_window);
	events_thread_done.set();
	events_thread.wait_to_finish();