Only allow moves if there is no winner

src/js/Game.js

@@ -256,6 +256,8 @@ export class Game
      * A value indicating whether the chip could be added.
      */
     addChip(x, y)
+    {
+        if (!this.winner)
         {
             for (let i = Game.#height - 1; i >= 0; i--)
             {
@@ -265,6 +267,7 @@ export class Game
                     return true;
                 }
             }
+        }
 
         return false;
     }