archive: do not let on-disk mode leak to zip archives
When the "--add-file" option is used to add the contents from an
untracked file to the archive, the permission mode bits for these
files are sent to the archive-backend specific "write_entry()"
method as-is. We normalize the mode bits for tracked files way
before we pass them to the write_entry() method; we should do the
same here.
This is not strictly needed for "tar" archive-backend, as it has its
own code to further clean them up, but "zip" archive-backend is not
so well prepared.
Signed-off-by: Junio C Hamano <gitster@pobox.com>