Ticket 628 - crash in aci evaluation
Bug Description: When trying to get effective rights on a entry that does not exist,
can lead to a crash from dereferencing a NULL pointer.
Fix Description: Check for NULL entry pointers and return the appropriate error.
https://fedorahosted.org/389/ticket/628
Reviewed by: nhosoi(Thanks Noriko!)
(cherry picked from commit ac8ceb91e42c31672147018d9d654879970dd38d)