Ticket 47771 - Move parentsdn initialization to avoid crash
Bug Description: It's possible to call slapi_sdn_done() before parentsdn is
initialized - which will crash the server.
Fix Description: Initialize parentsdn at the top of the function.
https://fedorahosted.org/389/ticket/47771
Reviewed by: nhosoi(Thanks!)
(cherry picked from commit 991984f1544c096d46a54ed3117542e8c5f3d70c)