better lock handling

pkg/actor/disk_storage.go

@@ -176,11 +176,12 @@ func (s *DiskStorage[V]) closeWriters() {
 	defer s.writersMu.Unlock()
 	for id, w := range s.writers {
 		w.mu.Lock()
+		w.purged = true
 		if err := w.file.Close(); err != nil {
 			log.Printf("failed to close event log %d: %v", id, err)
 		}
-		w.mu.Unlock()
 		delete(s.writers, id)
+		w.mu.Unlock()
 	}
 }