lib: remember empty-nonterm as zone cuts
In some cases like co.jp
, all queries below that are going to ask for it again.
They should be flagged as closest non-terminal and reuse authority's nameservers.
Example:
- Query
A abcd.co.jp
(queriesjp., co.jp., abcd.co.jp
) - Query
A efgh.co.jp
(queriesco.jp., efgh.co.jp
, while it should know thatco.jp
is an empty non-term)