Resolve WES-88 "Scoreboard"

Assets/SpellingBee/Scripts/GameController.cs

@@ -370,6 +370,8 @@ public partial class GameController : MonoBehaviour
     /// <param name="successful">true if the letter was correctly signed, false otherwise</param>
     public void NextLetter(bool successful)
     {
+        if (gameEnded) { return; }
+
         // Change color of current letter (skip spaces)
         if (successful)
         {