MB-100: correctly reach for errorsCell in buckets dialog

Change-Id: I4200ece0f6a4518aa91bdb8b328889fb10d867e6
Reviewed-on: http://review.couchbase.org/27554
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>