write_loose_object: don't bother trying to read an old object

write_loose_object: don't bother trying to read an old object

Before even calling this, all callers have done a "has_sha1_file(sha1)"
or "has_loose_object(sha1)" check, so there is no point in doing a
second check.

If something races with us on object creation, we handle that in the
final link() that moves it to the right place.

Signed-off-by: Linus Torvalds <redacted>
Signed-off-by: Junio C Hamano <redacted>