bugfix: don't throw error if zone change during IXFR answer init

src/knot/nameserver/ixfr.c

@@ -103,10 +103,10 @@ static int ixfr_load_chsets(journal_read_t **journal_read, zone_t *zone,
 		return ret;
 	} else if (!j_exists) {
 		return KNOT_ENOENT;
-	} else if (j_serial_to != serial_to) {
-		return KNOT_ERROR;
 	}
 
+	// please note that the journal serial_to might differ from zone SOA serial
+	// it is beacuse RCU lock is made at different moment than LMDB txn begin
 	return journal_read_begin(zone_journal(zone), false, serial_from, journal_read);
 }