NCBC-604: NullReferenceException in OperationBase`1.HandleClientError

Change-Id: If457e837fdda073b51b370a588863200910a29be
Reviewed-on: http://review.couchbase.org/40938
Tested-by: Jeffry Morris <jeffrymorris@gmail.com>
Reviewed-by: Brett Lawson <brett19@gmail.com>