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!)