Reference the correct variable in Thirties arrangement
Reference the correct variable in Thirties arrangement

There is no this._max_rows variable in the Thirties
arrangement since we don't maintain an internal
copy of that property. So previously we were
returning NaN for get_max_cards because _max_rows
was undefined. This fixes that.

https://phabricator.endlessm.com/T11233

endlessm/eos-knowledge-lib,endlessm/eos-knowledge-lib,endlessm/eos-knowledge-lib,endlessm/eos-knowledge-lib