833 datastream wrong end batch entry 2 (#841)

* refactor datastream server

* optimization and nil checks

* added a datastream check tool

* fix rpc to seqencer switching in datastream

* move batch end check after injected

* fix 0 batch gap bug

zk/datastream/server/data_stream_server_utils.go

@@ -138,7 +138,11 @@ func createBatchStartEntriesProto(
 	var err error
 	var batchStartEntries []DataStreamEntryProto
 
-	entries := NewDataStreamEntries(2 + int(3*(batchGap-1)) + len(gers))
+	batchGapEntriesCount := int(batchGap) - 1
+	if batchGapEntriesCount < 0 {
+		batchGapEntriesCount = 0
+	}
+	entries := NewDataStreamEntries(2 + 3*batchGapEntriesCount + len(gers))
 
 	// if we have a gap of more than 1 batch then we need to write in the batch start and ends for these empty batches
 	if batchGap > 1 {