DATAMONGO-829 - NearQuery should not default 'num' to zero.

NearQuery now ignores query.getLimit() equal to zero, when adding Query to NearQuery. This has to be done as limit is defaulted to zero within Query which then results in unintended propagation of the parameter.

In case 'num' should be explicitly set to zero one might use 'NearQuery.num(0)' as an alternative to the query approach.

Introduced 'null' check for 'NearQuery.query(Query)' and 'NearQuery.with(Pageable)' along the way.

Original Pull Request: #133