Fix crash when trying to apply invalid game model update

Not sure how this could happen but w/e

Packages/TTTKit/Sources/TTTKit/AI/GameModel.swift

@@ -62,7 +62,7 @@ public class GameModel: NSObject, NSCopying, GKGameModel {
         case .playAnywhere(update.mark), .playSpecific(update.mark, column: update.subBoard.column, row: update.subBoard.row):
             break
         default:
-            fatalError()
+            return
         }
         controller.play(on: update.subBoard, column: update.column, row: update.row)
     }