Zone expiration aborts transaction in progress

Fixes #929 (closed)

src/knot/events/handlers/expire.c

@@ -32,6 +32,7 @@ int event_expire(conf_t *conf, zone_t *zone)
 	log_zone_info(zone->name, "zone expired");
 
 	synchronize_rcu();
+	zone_control_clear(zone);
 	knot_sem_wait(&zone->cow_lock);
 	zone_contents_deep_free(expired);
 	knot_sem_post(&zone->cow_lock);