84614d9997 Unit test debug print of witness with empty instruction (Tobin C. Harding)
e96be5ee6e Fix Witness debug display bug (Tobin C. Harding)
Pull request description:
When we introduce a custom `Debug` implementation for the `Witness` we introduced a bug that causes code to panic if the witness contains an empty instruction.
The bug can be verified by putting patch 2 first or by running `cargo run --example sighash` on master.
ACKs for top commit:
apoelstra:
ACK 84614d9997
RCasatta:
ACK 84614d9997
Tree-SHA512: d51891206ab15f74dda07eb29ff3f6c69dc3f983a5a5abb55685688548481a19f7c1d33aa1183a89c553ff2bc86cf41057c2bae33d75e8a7f3b801056775bf9e