We should not return transaction metadata from `getrawtransaction` in case
transaction is not in the mempool. Height shouldn't be returned from
`gettransactionheight` in case transaction is in the mempool.
We had a kludge for getrawtransaction to set this useless field, but
7e371588a7 broke it. Add it right into the
decoder now to fix all types of queries (getblock/getrawtransaction/gettxout).
Fixes#1392.