Deleted LDAP groups no longer cause exceptions

When an LDAP group, or an organizational unit containing it, was deleted from the directory while it was still referenced — for example, held in a client's cache — accessing that group could throw an exception (LDAP result code 32, "noSuchObject") under particular cache states combined with bad timing. In the worst case this could affect access control and effectively break client sessions. Now the Content Server handles such exceptions and returns an empty result instead of rethrowing the exception, so that the operation continues normally.

(CMS-31183)