optimize execution speed

app/src/main/java/chess/controller/CommandExecutor.java

@@ -55,7 +55,7 @@ public class CommandExecutor {
 			case Moved:
 				boolean notifyPlayerTurn = true;
 				this.dispatcher.onBoardUpdate();
-				if (checkGameStatus()) {
+				if (!(command instanceof UndoCommand) && checkGameStatus()) {
 					this.dispatcher.onGameEnd();
 					notifyPlayerTurn = false;
 				}

app/src/main/java/chess/model/Game.java

@@ -70,6 +70,7 @@ public class Game {
 		playerTurn = Color.getEnemy(playerTurn);
 	}
 
+	// this is the bottleneck of algorithms using this chess engine
 	public GameStatus checkGameStatus(Color color) {
 		if (checkDraw())
 			return GameStatus.Draw;