Atomic: Draw on insufficient winning material when flagging.

[Happy0]

When a player flags on time in atomic chess, if their opponent does not having sufficient material to win, the game should be drawn.

Raised in: https://en.lichess.org/forum/general-chess-discussion/atomic-chess-endings?page=1

[ornicar]

Is it just about changing this line? https://github.com/ornicar/scalachess/blob/master/src/main/scala/variant/Atomic.scala#L123

[Happy0]

I don't think so. I think that would result in a draw before the guy capable of winning flagged on his clock due to these two lines:

https://github.com/ornicar/scalachess/blob/master/src/main/scala/Situation.scala#L29

https://github.com/ornicar/scalachess/blob/master/src/main/scala/Board.scala#L112

Now that you've drew attention to that, I've realised I should probably determine insufficient winning material polymorphically for variants rather than doing this:
https://github.com/ornicar/scalachess/blob/master/src/main/scala/variant/Atomic.scala#L119