Set HAS_MORE_PAGES flag when PagingState is null

If ResultSet.Metadata#setHasMorePages is called with a null PagingState, indicating that there are no more available results, we should explicitly unset the HAS_MORE_PAGES flag. This can be necessary where a custom QueryHandler implements its own LIMIT logic and wishes to send the signal to the client that the results are exhausted before the storage engine would normally do so.