Fix: Returns of non-terminal KuhnState was hardcoded for 2 players
Fix: Returns of non-terminal KuhnState was hardcoded for 2 players

KuhnState::Returns should return a std::vector with an entry for every player, but for any number of players this returns {0.0, 0.0} if the game isn't terminal. This was changed to return a vector of size num_players_ 
deepmind/open_spiel,deepmind/open_spiel,deepmind/open_spiel,deepmind/open_spiel,deepmind/open_spiel,deepmind/open_spiel