The fsck code has been slowly moving away from requiring an object struct in commits like 103fb6d43b (fsck: accept an oid instead of a "struct tag" for fsck_tag(), 2019-10-18), c5b4269b57 (fsck: accept an oid instead of a "struct commit" for fsck_commit(), 2019-10-18), etc. However, the only external interface that fsck.c provides is fsck_object(), which requires an object struct, then promptly discards everything except its oid and type. Let's factor out the post-discard part of that function as fsck_buffer(), leaving fsck_object() as a thin wrapper around it. That will provide more flexibility for callers which may not have a struct. Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>