TOMOYO: Accept \000 as a valid character.

TOMOYO 2.5 in Linux 3.2 and later handles Unix domain socket's address.
Thus, tomoyo_correct_word2() needs to accept \000 as a valid character, or
TOMOYO 2.5 cannot handle Unix domain's abstract socket address.

Reported-by: Steven Allen <steven@stebalien.com>
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
CC: stable@vger.kernel.org [3.2+]
Signed-off-by: James Morris <jmorris@namei.org>