create_tempfile: make sure that leading directories can be accessible by peers

create_tempfile: make sure that leading directories can be accessible by peers

In a shared repository, we should make sure adjust_shared_perm() is called
after creating the initial fan-out directories under objects/ directory.

Earlier an logico called the function only when mkdir() failed; we should
do so when mkdir() succeeded.

Signed-off-by: Junio C Hamano <gitster@pobox.com>