### 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)

WindowID window_id = MAIN_WINDOW_ID;
	
	for (const KeyValue<WindowID, WindowData> &E : windows) {
		if (event->xany.window == E.value.x11_window) {
			window_id = E.key;
			break;
		}
	}
	Rect2i new_rect;
	WindowData &wd = windows[window_id];
	if (wd.x11_window != event->xany.window) { 
		return;
	}
	
	wd.fullscreen = _window_fullscreen_check(window_id);
	wd.maximized = _window_maximize_check(window_id, "_NET_WM_STATE") && !wd.fullscreen;
	wd.minimized = _window_minimize_check(window_id) && !wd.fullscreen && !wd.maximized;
	
	Window root, parent, *children;
	unsigned int nchildren;
	if (XQueryTree(x11_display, wd.x11_window, &root, &parent, &children, &nchildren) && wd.parent != parent) {
		wd.parent = parent;
		window_set_position(wd.position, window_id);
	}
	XFree(children);
	{
		
		int x = 0, y = 0;
		Window child;
		XTranslateCoordinates(x11_display, wd.x11_window, DefaultRootWindow(x11_display), 0, 0, &x, &y, &child);