fixes in Game.java and UserInterface.java

src/main/java/ch/zhaw/pm2/racetrack/Game.java

@@ -187,6 +187,7 @@ public class Game implements GameSpecification {
             if(winner != NO_WINNER) {
                 return winner;
             }
+            switchToNextActiveCar();
         } while (!allCarsCrashed());
         return NO_WINNER;
     }