grep: fix exit status if external_grep() punts
grep: fix exit status if external_grep() punts

If external_grep() is called and punts, grep_cache() mistakenly reported a
hit, even if there were none.  The bug can be triggered by calling "git
grep --no-color" from a subdirectory.

Signed-off-by: Clemens Buchacher <3561697699be488d2983f82b126a1881ffc3afbc@aon.at>
Signed-off-by: Junio C Hamano <a6723cc3f76163bf7adb636a73ac3b0ceb3e6b9b@pobox.com>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git