### 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 (config_name.length() == 0) {
				class_str = "Godot_Engine";
			} else {
				class_str = config_name.utf8();
			}
		} else {
			class_str = "Godot";
		}
		classHint->res_class = class_str.ptrw();
		classHint->res_name = name_str.ptrw();
		XSetClassHint(x11_display, wd.x11_window, classHint);
		XFree(classHint);
	}
}
void DisplayServerX11::set_context(Context p_context) {
	_THREAD_SAFE_METHOD_
	context = p_context;
	for (KeyValue<WindowID, WindowData> &E : windows) {
		_update_context(E.value);
	}
}
void DisplayServerX11::set_native_icon(const String &p_filename) {
	WARN_PRINT("Native icon not supported by this display server.");
}
bool g_set_icon_error = false;
int set_icon_errorhandler(Display *dpy, XErrorEvent *ev) {
	g_set_icon_error = true;
	return 0;
}
void DisplayServerX11::set_icon(const Ref<Image> &p_icon) {