Ticket 47858 - Internal searches using OP_FLAG_REVERSE_CANDIDATE_ORDER can crash the server
Bug Description: If an internal search uses OP_FLAG_REVERSE_CANDIDATE_ORDER, and
the search fails tro find any candidates the server will crash.
Fix Description: Make sure we do not dereference a NULL sr_candidates pointer in
ldbm_search().
https://fedorahosted.org/389/ticket/47858
Reviewed by: rmeggins(Thanks!)
(cherry picked from commit e6cee31aa2beb6496df86490776f1f93d3a8348b)