[BUG] git cherry-pick does not complain about unknown options

Hi,

I was trying to cherry pick commits, while simultaneously changing the author. Unfortunately, cherry-pick doesn't have the same --author option as git-commit. However, instead of complaining about unknown option:

- when trying to cherry-pick one commit, it reported a BUG
- when trying to cherry-pick several commits, cherry-pick silently
  did nothing

All commits in tests existed in repository:

    $ git cherry-pick --author='TEST' <one-commit> # case 1
    error: BUG: expected exactly one commit from walk
    fatal: cherry-pick failed
    $ echo $?
    128
    $ git cherry-pick --author='TEST' <commit1> <commit2>  # case 2
    $ echo $?
    0
    $ git --version
    git version 2.18.0.windows.1

I've encountered this issue in Windows version, and Johannes Schindelin has confirmed that the issue is also present in Linux version.

Originally reported here: https://github.com/git-for-windows/git/issues/1751

-- Best regards, Andrei Rybak