shortlog: disallow left-over arguments outside repo

shortlog: disallow left-over arguments outside repo

If we are outside a repo and have any arguments left after
option-parsing, `setup_revisions()` will try to do its job and
something like this will happen:

$ git shortlog v2.16.0..
BUG: environment.c:183: git environment hasn't been setup
Aborted (core dumped)

The usage is wrong, but we could obviously handle this better. Note that
commit abe549e179 (shortlog: do not require to run from inside a git
repository, 2008-03-14) explicitly enabled `git shortlog` to run from
outside a repo, since we do not need a repo for parsing data from stdin.

Disallow left-over arguments when run from outside a repo.

Signed-off-by: Martin Ågren <martin.agren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>