Fix for empty NSID allocation.

src/knot/server/zones.c

@@ -1604,8 +1604,6 @@ int zones_normal_query_answer(knot_nameserver_t *nameserver,
 			rcu_read_unlock();
 			return KNOT_EOK;
 		}
-		knot_ns_error_response_full(nameserver, resp, rcode, resp_wire,
-		                            rsize);
 	} else {
 		/*
 		 * Now we have zone. Verify TSIG if it is in the packet.

src/libknot/packet/response.c

@@ -404,7 +404,7 @@ int knot_response_add_opt(knot_packet_t *resp,
 	 * other options are supported.
 	 */
 
-	if (add_nsid) {
+	if (add_nsid && opt_rr->option_count > 0) {
 		resp->opt_rr.option_count = opt_rr->option_count;
 		assert(resp->opt_rr.options == NULL);
 		resp->opt_rr.options = (knot_opt_option_t *)malloc(