ChessGame: fix type issue in tryAlgebraicMove
ChessGame: fix type issue in tryAlgebraicMove

Setting `$pawnPromotionPiece = null` raises the following Scrutinizer
error:

> It seems like `$pawnPromotionPiece` can also be of type `null`;
> however, parameter `$pawnPromotionPiece` of `ChessGame::tryMove()`
> does only seem to accept `integer`, maybe add an additional type
> check?

Instead of using `null`, we can use `ChessPiece::QUEEN`. If there
is a promotion, it should be part of the algebraic move, but if not
then defaulting to Queen promotion is a sensible fallback.

hemberger/smr,hemberger/smr,smrealms/smr,hemberger/smr,hemberger/smr,smrealms/smr,smrealms/smr