b4 review silently freezes on patatt fail

Hi Konstantin,

I noticed a bug in b4 review (as pinged on fedi but better to send the bug
report properly :)

So I had an incorrect configuration locally - my signing key in git (git config
user.signingKey) was set to the wrong one (the old, revoked one, the one
I... err... lost the private key for :P).

And with this in place, I was using b4 review tui --email-dry-run to experiment
with composing a reply.

The replying bit worked fine. But when I hit 'S' to send it froze up. No error
shown, just frozen.

Some strace's later and I identified that gpg (of course) was to blame - it
seems the python code just hangs waiting forever (idle event loop looks like).

And it seems to be when it tried to use patatt to sign my reply to a mail, gpg
failed with exit code 2:

execve("/usr/bin/gpg", ["gpg", "--batch", "--no-auto-key-retrieve",
"--no-auto-check-trustdb", "-s", "-u", "130EC0891A27271B"]) = 0
exit_group(2)

(I can give you a full strace if you need!)

I confirmed this was the signing for sure as passing --no-sign fixed it.

Once I updated my signing key to the correct one, everything worked fine.

$ b4 --version
0.15.2

Cheers, Lorenzo