don't crash terse_bucket_info_uploader on missing bucket

Change-Id: I238bb373644798ba052b05099df7998a2cd22fd3
Reviewed-on: http://review.couchbase.org/42360
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>