fix: reset connection state when joining a session failed

Author: FabianStoll

Assets/Scripts/Gameplay/UI/Session/SessionUIMediator.cs

@@ -194,6 +194,7 @@ void HandleSessionJoinResult((bool Success, ISession Session) result)
             }
             else
             {
+                m_ConnectionManager.RequestShutdown();
                 UnblockUIAfterLoadingIsComplete();
             }
         }