fix error when game end🐛

[Rouzip]

When game ends, it still calls

        def _process_state_and_get_action(self, state, gameover):
            self.get_grid_from_state(state)     # there

            actions = self.get_action(state, gameover)

            if gameover:
                return None
            else:
                return self._filter_invalid_actions(actions, state)

It will make errors because state doesn't have property "pgs".