CCBC-866: check cached provider isn't NULL
CCBC-866: check cached provider isn't NULL

Change-Id: Ic86a3d0f738ae581713c48aad38492b46f4655a5
Reviewed-on: http://review.couchbase.org/94732
Reviewed-by: Sergey Avseyev <87f6d5e4fd3644c3c20800cde7fd3ad1569370b3@gmail.com>
Tested-by: Build Bot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>

kojiromike/libcouchbase,kojiromike/libcouchbase,avsej/libcouchbase,avsej/libcouchbase,couchbase/libcouchbase,couchbase/libcouchbase,couchbase/libcouchbase,avsej/libcouchbase,couchbase/libcouchbase,avsej/libcouchbase,couchbase/libcouchbase,couchbase/libcouchbase,kojiromike/libcouchbase,couchbase/libcouchbase,avsej/libcouchbase,avsej/libcouchbase,avsej/libcouchbase,kojiromike/libcouchbase