s3: smbd: vfs_dirsort module.

Fix an off-by-one check that would cause seekdir to
seek off the end of the cached array.

Signed-off-by: Jeremy Allison <jra@samba.org>
Reviewed-by: Ronnie Sahlberg <ronniesahlberg.gmail.com>

Autobuild-User(master): Jeremy Allison <jra@samba.org>
Autobuild-Date(master): Wed Sep  3 19:59:54 CEST 2014 on sn-devel-104