Remove useless condition in KXK endgame

Because eval is never called when in check.

No functional change.
Fix crash when reaching max ply

Bug introduced in 1b7223a53c419212efbd that
updated the ss base stack without increasing
the dimension.

No functional change.
Merge remote-tracking branch 'upstream/master' into AlwaysDancing
Merge branch 'AlwaysDancing' of https://github.com/Kingdefender/Stockfish into AlwaysDancing