remove message during delivery when we encounter an error after havin…

…g placed the message in the destination path

before, we would leave the file, but rollback the delivery. future deliveries
would attempt to deliver to the same path, but would fail because a file
already exists.

encountered during testing on windows, not during actual operation. though it
could in theory have happened.

store/account.go

@@ -1349,13 +1349,17 @@ func (a *Account) DeliverMessage(log *mlog.Log, tx *bstore.Tx, m *Message, msgFi
 
 	if sync {
 		if err := moxio.SyncDir(msgDir); err != nil {
+			xerr := os.Remove(msgPath)
+			log.Check(xerr, "removing message after syncdir error", mlog.Field("path", msgPath))
 			return fmt.Errorf("sync directory: %w", err)
 		}
 	}
 
 	if !notrain && m.NeedsTraining() {
 		l := []Message{*m}
 		if err := a.RetrainMessages(context.TODO(), log, tx, l, false); err != nil {
+			xerr := os.Remove(msgPath)
+			log.Check(xerr, "removing message after syncdir error", mlog.Field("path", msgPath))
 			return fmt.Errorf("training junkfilter: %w", err)
 		}
 		*m = l[0]