events: fixed re-planning dnssec after empty update

src/knot/events/handlers/dnssec.c

@@ -48,10 +48,6 @@ void event_dnssec_reschedule(conf_t *conf, zone_t *zone,
 		refresh_at = refresh->next_rollover;
 	}
 
-	if (refresh_at <= 0) {
-		return;
-	}
-
 	log_dnssec_next(zone->name, (time_t)refresh_at);
 
 	if (refresh->plan_ds_query) {
@@ -63,7 +59,7 @@ void event_dnssec_reschedule(conf_t *conf, zone_t *zone,
 	}
 
 	zone_events_schedule_at(zone,
-		ZONE_EVENT_DNSSEC, (time_t)refresh_at,
+		ZONE_EVENT_DNSSEC, refresh_at ? (time_t)refresh_at : ignore,
 		ZONE_EVENT_PARENT_DS_Q, refresh->plan_ds_query ? now : ignore,
 		ZONE_EVENT_NSEC3RESALT, refresh->next_nsec3resalt ? refresh->next_nsec3resalt : ignore,
 		ZONE_EVENT_NOTIFY, zone_changed ? now : ignore