Berkeley DB uses 1 based indices for RECNO databases, and the
implementation of BlockchainDB for Berkeley DB assumes 1 based
indices are passed to the API, whereas the LMDB one assumes
0 based indices. This is all internally consisteny, but since
the BDB code stores 1 based indices in the database, external
users have to be aware of this, as the indices will be off by
one depending on which DB is used.