NULL for numeric fields -> NaN

Hi!

On the same setup as in https://gist.github.com/929626 :

```
create table foo(id bigint, num bigint);
insert into foo(id) values(1);
```

...
    db.query('select \* from foo').on('row', function(row){
      console.log(row); // ---> {id: 1, num: NaN}
    });

Can you confirm the issue?

TIA,
--Vladimir
