Fix PhantomTTT::MaxGameLength

The max game length of an phantom TTT relies on the max length
of its underlying TTT game. Encapsulate this instead of re-
implementing TicTacToe::MaxGameLenth in PhantomTTT::MaxGameLenth.

Signed-off-by: odanrc <odanrc@yahoo.com.br>

open_spiel/games/phantom_ttt/phantom_ttt.h

@@ -118,7 +118,7 @@ class PhantomTTTGame : public Game {
   // These will depend on the obstype parameter.
   std::vector<int> InformationStateTensorShape() const override;
   std::vector<int> ObservationTensorShape() const override;
-  int MaxGameLength() const override { return tic_tac_toe::kNumCells * 2 - 1; }
+  int MaxGameLength() const override { return game_->MaxGameLength() * 2 - 1; }
 
   ObservationType obs_type() const { return obs_type_; }