Icinga DB downtime history: provide cancel_time where has_been_cancel…

…led may be 1

The table sla_history_downtime requires a downtime_end.
The Go daemon takes the cancel_time if has_been_cancelled is 1.
So we must supply a cancel_time whereever has_been_cancelled is 1.
Otherwise the Go daemon can't process some entries.

lib/icingadb/icingadb-objects.cpp

@@ -1860,6 +1860,7 @@ void IcingaDB::SendStartedDowntime(const Downtime::Ptr& downtime)
 		"scheduled_end_time", Convert::ToString(TimestampToMilliseconds(downtime->GetEndTime())),
 		"has_been_cancelled", Convert::ToString((unsigned short)downtime->GetWasCancelled()),
 		"trigger_time", Convert::ToString(TimestampToMilliseconds(downtime->GetTriggerTime())),
+		"cancel_time", Convert::ToString(TimestampToMilliseconds(downtime->GetRemoveTime())),
 		"event_id", CalcEventID("downtime_start", downtime),
 		"event_type", "downtime_start"
 	});