Fix logout current connection crash

Make sure that the neochat can handle switching connection when the current one is logged out. This is mostly about using QPointer to handle use after free issues due to room objects being deleted.

src/models/messageeventmodel.h

@@ -113,7 +113,7 @@ private Q_SLOTS:
     void refreshRow(int row);
 
 private:
-    NeoChatRoom *m_currentRoom = nullptr;
+    QPointer<NeoChatRoom> m_currentRoom = nullptr;
     QString lastReadEventId;
     QPersistentModelIndex m_lastReadEventIndex;
     int rowBelowInserted = -1;