Bug 617630 - fix coverify Defect Type: Resource leaks issues CID 12052 - 12093

https://bugzilla.redhat.com/show_bug.cgi?id=617630
Resolves: bug 617630
Bug description: fix coverify Defect Type: Resource leaks issues CID 12066.
description: The usn_preop_delete() has been modified to release csn when an error occurs.

ldap/servers/plugins/usn/usn.c

@@ -290,6 +290,7 @@ usn_preop_delete(Slapi_PBlock *pb)
         if (CSN_SUCCESS != rc) {
             slapi_log_error(SLAPI_LOG_FATAL, USN_PLUGIN_SUBSYSTEM,
                             "usn_preop_delete: csngen_new failed (%d)\n", rc);
+            csngen_free(&csn);
             goto bail;
         }
         operation_set_csn(op, csn);