fix: remove stored sessions when clients get disconnected by the server

Server/src/main/java/uulm/teamname/marvelous/server/lobbymanager/LobbyManager.java

@@ -143,6 +143,10 @@ public class LobbyManager {
             return;
         }
 
+        if(!byRemote) {
+            participants.remove(client.id);
+        }
+
         Participant participant = participants.get(client.id);
 
         LobbyConnection lobby = lobbies.get(participant.lobby);