When a non-existing group is refered from a domain, the permissions detail screen should warn the user about this.

When a non-existing group is refered from a domain, the group is still shown on the permission detail screen. This doesn't break anything, but it would be nice if a user gets feedback on this "data inconsistency" and possible "security risk".

Because if someone would recreate a group with that name, that group would have some permissions that aren't expected.