tomoyo: cleanup. don't store bogus pointer

If domain is NULL then &domain->list is a bogus address.  Let's leave
head->r.domain NULL instead of saving an unusable pointer.

This is just a cleanup.  The current code always checks head->r.eof
before dereferencing head->r.domain.

Signed-off-by: Dan Carpenter <error27@gmail.com>
Acked-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>