### 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)

_THREAD_SAFE_METHOD_
	ERR_FAIL_COND_V(!windows.has(p_window), Size2i());
	const WindowData &wd = windows[p_window];
	if (wd.fullscreen) {
		return wd.size;
	}
	XWindowAttributes xwa;
	XSync(x11_display, False);
	XGetWindowAttributes(x11_display, wd.x11_window, &xwa);
	int w = xwa.width;
	int h = xwa.height;
	Atom prop = XInternAtom(x11_display, "_NET_FRAME_EXTENTS", True);
	if (prop != None) {
		Atom type;
		int format;
		unsigned long len;
		unsigned long remaining;
		unsigned char *data = nullptr;
		if (XGetWindowProperty(x11_display, wd.x11_window, prop, 0, 4, False, AnyPropertyType, &type, &format, &len, &remaining, &data) == Success) {
			if (format == 32 && len == 4 && data) {
				long *extents = (long *)data;
				w += extents[0] + extents[1]; 
				h += extents[2] + extents[3]; 
			}
			XFree(data);
		}
	}
	return Size2i(w, h);
}
bool DisplayServerX11::_window_maximize_check(WindowID p_window, const char *p_atom_name) const {