[FS9] Fix a crash (pure virtual call)

src/plugins/simulator/fs9/fs9client.cpp

@@ -169,6 +169,10 @@ namespace BlackSimPlugin
         {
             closeConnection();
             SafeRelease(m_hostAddress);
+
+            // This needs to be disconnected before calling the base class destructor,
+            // otherwise the slot can be called after the derived class is destroyed.
+            disconnect(this, &CFs9Client::connectionComplete, this, &CFs9Client::handleConnectionCompleted);
         }
 
         void CFs9Client::sendTextMessage(const QString &textMessage)