viced: Print a warning when using a deleted client

viced: Print a warning when using a deleted client

We should never get a deleted client back from GetClient. Log a
message if we do, to explain why access may suddenly appear to fail,
and assist in determining why.

Note that we still try to service the request, since the accessing
user may still have enough access to do whatever was requested.

Reviewed-on: http://gerrit.openafs.org/4529
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
(cherry picked from commit 8b07814e037d19dc9868dd202e82d69b96fbdcae)

Change-Id: I0b1d9fe46e5b83b93b59ff6facc2421db9136c12
Reviewed-on: http://gerrit.openafs.org/4533
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>