ixfr/axfr: failover even when the ixfr reply wasn't valid

before: ixfr falls back to axfr only if valid, but negative reply, e.g. NOTAUTH, journal inconsistency..
after: ixfr falls back to axfr in any case ixfr fails, e.g. malformed reply packet

src/knot/events/handlers/refresh.c

@@ -405,6 +405,7 @@ static void ixfr_cleanup(struct refresh_data *data)
 	}
 
 	knot_rrset_free(data->ixfr.final_soa, data->mm);
+	data->ixfr.final_soa = NULL;
 	mm_free(data->mm, data->ixfr.proc);
 	data->ixfr.proc = NULL;
 
@@ -952,16 +953,6 @@ static int transfer_consume(knot_layer_t *layer, knot_pkt_t *pkt)
 		}
 	}
 
-	// IXFR to AXFR failover
-	if (data->xfr_type == XFR_TYPE_IXFR && next == KNOT_STATE_FAIL) {
-		REFRESH_LOG(LOG_WARNING, data->zone->name, data->remote,
-		            "fallback to AXFR");
-		ixfr_cleanup(data);
-		layer->flags |= KNOT_RQ_LAYER_CLOSE;
-		data->xfr_type = XFR_TYPE_AXFR;
-		return KNOT_STATE_RESET;
-	}
-
 	return next;
 }
 
@@ -1087,7 +1078,18 @@ static int try_refresh(conf_t *conf, zone_t *zone, const conf_remote_t *master,
 
 	int timeout = conf->cache.srv_tcp_reply_timeout * 1000;
 
-	int ret = knot_requestor_exec(&requestor, req, timeout);
+	int ret;
+
+	// while loop runs 0x or 1x; IXFR to AXFR failover
+	while ((ret = knot_requestor_exec(&requestor, req, timeout)) != KNOT_EOK &&
+	       data.xfr_type == XFR_TYPE_IXFR) {
+		REFRESH_LOG(LOG_WARNING, data.zone->name, data.remote,
+		            "fallback to AXFR");
+		ixfr_cleanup(&data);
+		data.xfr_type = XFR_TYPE_AXFR;
+		requestor.layer.state = KNOT_STATE_RESET;
+		requestor.layer.flags |= KNOT_RQ_LAYER_CLOSE;
+	}
 	knot_request_free(req, NULL);
 	knot_requestor_clear(&requestor);