libselinux: Fix selabel_open(3) services if no digest requested

If selabel_open is called with no request for a digest it will fail
with ENOENT. This fixes all the labeling routines to resolve this
problem. The utils/selabel_digest example has also been updated
to allow calling selabel_open with and without digest requests to
aid testing.

Signed-off-by: Richard Haines <richard_c_haines@btinternet.com>
8 files changed