609255 - fix coverity Defect Type: Memory - illegal accesses issues

https://bugzilla.redhat.com/show_bug.cgi?id=609255

12222 UNINIT Triaged Unassigned Bug Minor Fix Required
replica_get_purl_for_op() ds/ldap/servers/plugins/replication/repl5_plugins.c

Comment:
In case of an error "cannot obtain consumer connection extension or supplier_ruv", uninitialized purl is returned to the caller.  Init purl to NULL

ldap/servers/plugins/replication/repl5_plugins.c

@@ -1298,7 +1298,7 @@ is_mmr_replica (Slapi_PBlock *pb)
 static const char *replica_get_purl_for_op (const Replica *r, Slapi_PBlock *pb, const CSN *opcsn)
 {
     int is_replicated_op;
-    const char *purl;
+    const char *purl = NULL;
 
     slapi_pblock_get(pb, SLAPI_IS_MMR_REPLICATED_OPERATION, &is_replicated_op);