avoid empty spaces in file name

weed/mq/broker/broker_grpc_configure.go

@@ -113,7 +113,7 @@ func (b *MessageQueueBroker) AssignTopicPartitions(c context.Context, request *m
 func (b *MessageQueueBroker) genLogFlushFunc(t *mq_pb.Topic, partition *mq_pb.Partition) log_buffer.LogFlushFuncType {
 	topicDir := fmt.Sprintf("%s/%s/%s", filer.TopicsDir, t.Namespace, t.Name)
 	partitionGeneration := time.Unix(0, partition.UnixTimeNs).UTC().Format(topic.TIME_FORMAT)
-	partitionDir := fmt.Sprintf("%s/%s/%4d-%4d", topicDir, partitionGeneration, partition.RangeStart, partition.RangeStop)
+	partitionDir := fmt.Sprintf("%s/%s/%04d-%04d", topicDir, partitionGeneration, partition.RangeStart, partition.RangeStop)
 
 	return func(startTime, stopTime time.Time, buf []byte) {
 		if len(buf) == 0 {