fix: added check to setGameWinner to only allow one of the team playing or none to be the winner

src/main/java/cz/muni/fi/pa165/icehockeymanager/services/GameServiceImpl.java

 package cz.muni.fi.pa165.icehockeymanager.services;
 
 import cz.muni.fi.pa165.icehockeymanager.dao.GameDao;
+import cz.muni.fi.pa165.icehockeymanager.exceptions.UnknownTeamException;
 import cz.muni.fi.pa165.icehockeymanager.model.Game;
 import cz.muni.fi.pa165.icehockeymanager.model.Team;
 import org.springframework.beans.factory.annotation.Autowired;
@@ -57,6 +58,9 @@ public class GameServiceImpl implements GameService {
 
     @Override
     public void setGameWinner(Game game, Team team) {
+        if (team != null &&!team.equals(game.getHomeTeam()) && !team.equals(game.getAwayTeam())) {
+            throw new UnknownTeamException("The winner is not part of this game");
+        }
         game.setWinner(team);
         gameDao.update(game);
     }