CBSE-1487/MB-12569: Ignore empty bucket

Change-Id: I535646d1731f543678a6fdf97eb5acb981a1e5cb
Reviewed-on: http://review.couchbase.org/42909
Reviewed-by: Bin Cui <bin.cui@gmail.com>
Tested-by: Bin Cui <bin.cui@gmail.com>