Ticket #48216 - crash in ns-slapd when deleting winSyncSubtreePair from sync agreement
Description: In free_subtree_pairs, the condition for stopping the
loop to clean up the AD and DS subtree dn was incomplete.
This patch checks the AD and DS subtree dn and if any of the pair
is NULL, it stops the clean up. Related to the issue, more checks
for the validation of the winSyncSubtreePair is added so that any
single valued cases are ignored with an error log.
[single valued case examples]
winSyncSubtreePair: ou=People,dc=anytree
winSyncSubtreePair: ou=People,dc=anytree:
winSyncSubtreePair: :ou=People,dc=anytree
https://fedorahosted.org/389/ticket/48216
Reviewed by rmeggins@redht.com (Thank you, Rich!!)