### 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)

const WindowData &wd = windows[p_window];
	if (wd.fullscreen && !_window_fullscreen_check(p_window)) {
		_set_wm_fullscreen(p_window, true, wd.exclusive_fullscreen);
	} else if (wd.maximized && !_window_maximize_check(p_window, "_NET_WM_STATE")) {
		_set_wm_maximized(p_window, true);
	} else if (wd.minimized && !_window_minimize_check(p_window)) {
		_set_wm_minimized(p_window, true);
	}
	if (wd.on_top) {
		Atom wm_state = XInternAtom(x11_display, "_NET_WM_STATE", False);
		Atom wm_above = XInternAtom(x11_display, "_NET_WM_STATE_ABOVE", False);
		XClientMessageEvent xev;
		memset(&xev, 0, sizeof(xev));
		xev.type = ClientMessage;
		xev.window = wd.x11_window;
		xev.message_type = wm_state;
		xev.format = 32;
		xev.data.l[0] = _NET_WM_STATE_ADD;
		xev.data.l[1] = wm_above;
		xev.data.l[3] = 1;
		XSendEvent(x11_display, DefaultRootWindow(x11_display), False, SubstructureRedirectMask | SubstructureNotifyMask, (XEvent *)&xev);
	}
}
bool DisplayServerX11::window_is_maximize_allowed(WindowID p_window) const {
	_THREAD_SAFE_METHOD_
	return _window_maximize_check(p_window, "_NET_WM_ALLOWED_ACTIONS");
}
void DisplayServerX11::_set_wm_maximized(WindowID p_window, bool p_enabled) {