fix: add splitscreen, fix dlcs not loading, major RCE vuln fix on packet net, fix chunk loading on non-server clients, persistent saves

note: I changed how XUID works, player data might be wiped on old saves, save items on a chest or similar before trying to load old saves on new version

Minecraft.Client/ServerLevel.cpp

@@ -982,7 +982,9 @@ void ServerLevel::entityRemoved(shared_ptr<Entity> e)
 
 shared_ptr<Entity> ServerLevel::getEntity(int id)
 {
-	return entitiesById[id];
+	AUTO_VAR(it, entitiesById.find(id));
+	if(it != entitiesById.end()) return it->second;
+	return nullptr;
 }
 
 bool ServerLevel::addGlobalEntity(shared_ptr<Entity> e)