[Backport to 3.2] menu items are moved incorrectly

When introducing the menu editor's Advanced Settings for CMS 10.2, the change appears to have broken the moving of root-level menu items if the menu is setup with an hst:prototypeitem as documented here [1]. This is a regression compared to CMS 10.1, but only happens when a editable menu has been setup (manually) with a prototype item, which is not common.

The issue has been detected when testing CMS 11.0 (new channel manager) and is fixed for 11.0. We need to decide if and when we should back-port this fix.

[1] https://www.onehippo.org/library/concepts/hst-configuration-model/sitemenu-configuration.html