BUG/MEDIUM: acl: boolean only matches were broken by recent changes

The ACL changes made in the last patchset force the execution
of each pattern matching function. The function pat_match_nothing
was not provided to be excuted, it was just used as a flag that
was checked by the ACL execution code. Now this function is
executed and always returns false.

This patch makes it work as expected. Now, it returns the boolean
status of the received sample just as was done previously in the
ACL code.

This bug is a part of the patchset just merged. It does not need
to be backported.