Fix txs with lock_time but max sequence

[mhanne]

Some transactions have a lock_time set, but none of the input sequences is < max. When the lock_time is also in the block range, it tries to lookup a block that might not yet exist. See for example: https://test.webbtc.com/tx/2c2c73f5efa19e0fb3c96ba0215d44326405f102c7d207a9d8956f4de6772e92.json