### 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)

for (int i = 0; i < CURSOR_MAX; i++) {
		if (cursors[i] != None) {
			XFreeCursor(x11_display, cursors[i]);
		}
		if (cursor_img[i] != nullptr) {
			XcursorImageDestroy(cursor_img[i]);
		}
	}
	if (xim) {
		XCloseIM(xim);
	}
	XCloseDisplay(x11_display);
	if (xmbstring) {
		memfree(xmbstring);
	}
#ifdef SPEECHD_ENABLED
	if (tts) {
		memdelete(tts);
	}
#endif
#ifdef DBUS_ENABLED
	memdelete(screensaver);
	memdelete(portal_desktop);
#endif
}
void DisplayServerX11::register_x11_driver() {
	register_create_function("x11", create_func, get_rendering_drivers_func);
}
#endif