rplan: fix a coverity warning (CID 164834)

There would be no real resource leak, as the memory is on a mempool,
so the lifetime is limited by kr_request finishing.  Also, it's only
on an unlikely error branch, but still...

lib/rplan.c

@@ -143,6 +143,7 @@ static struct kr_query *kr_rplan_push_query(struct kr_rplan *rplan,
 	if (parent && (parent->flags & qry->flags & QUERY_FORWARD)) {
 		ret = kr_nsrep_copy_set(&qry->ns, &parent->ns);
 		if (ret) {
+			query_free(rplan->pool, qry);
 			return NULL;
 		}
 	}