fix close if no queue is used

pkg/actor/disk_storage.go

@@ -104,7 +104,9 @@ func (s *DiskStorage[V]) LoadEvents(id uint64, grain Grain[V]) error {
 }
 
 func (s *DiskStorage[V]) Close() {
-	s.save()
+	if s.queue != nil {
+		s.save()
+	}
 	close(s.done)
 }