lib/validate: fixed memory bug

this code used memory pool of source packet instead
of the answer, this could result in invalidated
memory read if the memory occupied by source
packet was rewritten

lib/layer/validate.c

@@ -484,7 +484,7 @@ static int validate(knot_layer_t *ctx, knot_pkt_t *pkt)
 		const knot_pktsection_t *auth = knot_pkt_section(pkt, KNOT_AUTHORITY);
 		for (unsigned i = 0; i < auth->count; ++i) {
 			const knot_rrset_t *rr = knot_pkt_rr(auth, i);
-			kr_rrarray_add(&req->authority, rr, &pkt->mm);
+			kr_rrarray_add(&req->authority, rr, &req->answer->mm);
 		}
 	}