The index-pack command, when processing a thin pack, fixed up the pack
after-the-fact.  It forgets to fsync the result, because it only did that
in one path rather in all cases of fixup.

This moves the fsync_or_die() to the fix-up routine itself, rather than
doing it in one of the callers, so that all cases are covered.
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>