Ticket 47793 - Server crashes if uniqueMember is invalid syntax and memberOf
plugin is enabled.
Bug Description: MemberOf assumes the DN value has the correct syntax, and
does not check the normalized value of that DN. This
leads to dereferencing a NULL pointer and crash.
Fix Description: Check the normalized value, and log a proper error.
https://fedorahosted.org/389/ticket/47793
Reviewed by: nhosoi(Thanks!)
(cherry picked from commit 6816e1155b28fb65fe294099336c4acbbac8ad77)