fix othello player skip logic

src/board.rs

@@ -196,7 +196,10 @@ impl Board {
     }
 
     pub fn game_winner(&self, turn: Piece) -> Option<Piece> {
-        if self.possible_moves(turn).count() > 0 {
+        // Wikipedia: `Players take alternate turns. If one player cannot make a valid move, play passes back to the other player. The game ends when the grid has filled up or if neither player can make a valid move.`
+
+        if self.possible_moves(turn).next().is_some() || self.possible_moves(!turn).next().is_some()
+        {
             // player can still make a move, there is no winner
             return None;
         }