Add more validity checks at policy load time to reject malformed
policies and prevent subsequent out-of-range indexing when in permissive
mode.  Resolves the NULL pointer dereference reported in
https://bugzilla.redhat.com/show_bug.cgi?id=357541.
Signed-off-by: NStephen Smalley <sds@tycho.nsa.gov>
Signed-off-by: NJames Morris <jmorris@namei.org>