Inconsistent exit code for `git grep --files-without-match` with `--quiet`

[Anthony Sottile <asottile@xxxxxxxxx>]

Using the latest revision of git:

$ ./git --version
git version 2.14.GIT

$ ./git-grep --files-without-match nope -- blob.c; echo $?
blob.c
0

$ ./git-grep --files-without-match --quiet nope -- blob.c; echo $?
1

I expect both to exit 0

Note that blob.c does not contain "nope", here is the revision I am
using: https://github.com/git/git/blob/b3622a4ee94e4916cd05e6d96e41eeb36b941182/blob.c
-- this file / case isn't special I just picked a reproduction that
may be convenient for git developers.

Anthony