fix: changing piece on the kings square with chess.put()

[Manukyanq]

Hello! I want to make a chessboard, where users can manually set the position they need and thechess.put() and chess.remove() methods are superuseful for me. I found a tiny bug, which I can make work with small hack, but anyway it is confusing and will be nice to fix it.

Lets say I want manually swap white king's and white queen's positions.

const chess = new Chess()

const status1 = chess.put({ type: 'q', color: 'w' }, 'e1') // true
const status2 = chess.put({ type: 'k', color: 'w' }, 'd1') // false

but if I remove white king and only after then put queen and king it works without errors

const chess = new Chess()

chess.remove('e1')
const status1 = chess.put({ type: 'q', color: 'w' }, 'e1') // true
const status2 = chess.put({ type: 'k', color: 'w' }, 'd1') // true

I can provide more details if it is required. Thank you

[jhlywa]

Hi @Manukyanq, thanks for the PR!

I think I'm tracking the issue. Essentially, if you overwrite the position of the king with any other piece, we need to set the _kings entry (for the overwritten king color) to EMPTY. Could you add a comment to that section just to highlight the what's happening? A one-liner is fine.

Thanks and good find!

[jhlywa]

Merged. Thanks again!