Incorrect null move modification

```
    inline void doNullMove() {
        history.push_back(current_state);
        current_state.turn = ~current_state.turn;
        current_state.hash ^= zobrist::RandomTurn;
        current_state.fullMoveNumber += (current_state.turn == WHITE);
        current_state.pliesFromNull = current_state.repetition = 0;
        current_state.mv = Move::null();
    }
```
It doesn't clear the en passant.