* Rewrite GetData handling to match the zcashd implementation
`zcashd` silently ignores missing blocks, but sends found transactions
followed by a `NotFound` message:
e7b425298f/src/main.cpp (L5497)
This is significantly different to the behaviour expected by the old
Zebra connection state machine, which expected `NotFound` for blocks.
Also change Zebra's GetData responses to peer request so they ignore
missing blocks.
* Stop hanging on incomplete transaction or block responses
Instead, if the peer sends an unexpected block, unexpected transaction,
or NotFound message:
1. end the request, and return a partial response containing any items
that were successfully received
2. if none of the expected blocks or transactions were received, return
an error, and close the connection
b1f14f47c6