events: add zone_events_is_scheduled() API

src/knot/zone/events/events.c

@@ -282,6 +282,11 @@ void zone_events_schedule_at(zone_t *zone, zone_event_type_t type, time_t time)
 	pthread_mutex_unlock(&events->mx);
 }
 
+bool zone_events_is_scheduled(zone_t *zone, zone_event_type_t type)
+{
+	return zone_events_get_time(zone, type) > 0;
+}
+
 void zone_events_enqueue(zone_t *zone, zone_event_type_t type)
 {
 	if (!zone || !valid_event(type)) {

src/knot/zone/events/events.h

@@ -119,6 +119,14 @@ void zone_events_schedule_at(struct zone_t *zone, zone_event_type_t type, time_t
  */
 void zone_events_schedule(struct zone_t *zone, zone_event_type_t type, unsigned dt);
 
+/*!
+ * \brief Check if zone event is scheduled.
+ *
+ * \param zone  Zone to check event of.
+ * \param type  Type of event.
+ */
+bool zone_events_is_scheduled(struct zone_t *zone, zone_event_type_t type);
+
 /*!
  * \brief Cancel one zone event.
  *