don't crash upr_notifier if stream_request returns error

..just report the error to the caller

Change-Id: I9b53331103616b8e5d82b7a11a1a3c3a185a0cff
Reviewed-on: http://review.couchbase.org/37765
Reviewed-by: Artem Stemkovski <artem@couchbase.com>
Tested-by: Artem Stemkovski <artem@couchbase.com>