In a similar spirit as preceding patches to `git repack` and `git
pack-objects`, fix the identical problem in `git index-pack`.
Signed-off-by: Taylor Blau <me@ttaylorr.com> Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com> Signed-off-by: Taylor Blau <me@ttaylorr.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>