selinux: fix handling of uninitialized selinux state in get_bools/classes

If security_get_bools/classes are called before the selinux state is
initialized (i.e. before first policy load), then they should just
return immediately with no booleans/classes.

Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>
Signed-off-by: Paul Moore <paul@paul-moore.com>