rewrite indexer service in the attempt to fix failing test

https://github.com/tendermint/tendermint/pull/3227/#issuecomment-462316527

state/txindex/indexer_service.go

@@ -46,8 +46,13 @@ func (is *IndexerService) OnStart() error {
 			select {
 			case msg := <-blockHeadersSub.Out():
 				header := msg.Data().(types.EventDataNewBlockHeader).Header
+				if header.NumTxs == 0 {
+					continue
+				}
 				batch := NewBatch(header.NumTxs)
-				for i := int64(0); i < header.NumTxs; i++ {
+				i := int64(0)
+			TXS_LOOP:
+				for {
 					select {
 					case msg2 := <-txsSub.Out():
 						txResult := msg2.Data().(types.EventDataTx).TxResult
@@ -57,6 +62,10 @@ func (is *IndexerService) OnStart() error {
 								"index", txResult.Index,
 								"err", err)
 						}
+						i++
+						if i == header.NumTxs {
+							break TXS_LOOP
+						}
 					case <-txsSub.Cancelled():
 						is.Logger.Error("Failed to index block. txsSub was cancelled. Did the Tendermint stop?",
 							"height", header.Height,