[BUG] TransactionIndex fetch out of bound

[superhx]

Concurrent Problem:

1. [Thread1] ElasticTransactionIndex#append invoke stream.append , update the nextOffset=12478 but not assigned to lastAppend yet
2. [Thread2] ElasticTransactionIndex#iterator read the transaction index, get endPosition=12478 and lastAppend=12444 future
3. [Thread2] stream fetch out of bound