[R4R]Fix miningprefetcher

[qinglin89]

Description

panic with nil pointer of Transaction.inner

Rationale

If PrefetchMining run fast enough that sub-prefetcher-routines checked txCurr before transaction had been peeked from TransactionByPriceAndNonce at the main worker routine, it would get an empty Transaction struct with nil inner filed which would cause panic in func (s EIP155Signer) Sender(tx *Transaction) (common.Address, error)

Example

N/A

Changes

Notable changes:

• Instead of using empty Transaction for tx initialization, Peek the first transaction from TransactionByPriceAndNonce for current transaction txCurr at miner/worker.go:line787 which would be accessed in mining-prefetcher-routine