Fix singleton class ownership

We shouldn't allow Qt parent ownership in here.

src/app/application.cpp

@@ -550,7 +550,7 @@ int Application::exec(const QStringList &params)
 #ifndef DISABLE_COUNTRIES_RESOLUTION
         Net::GeoIPManager::initInstance();
 #endif
-        ScanFoldersModel::initInstance(this);
+        ScanFoldersModel::initInstance();
 
 #ifndef DISABLE_WEBUI
         m_webui = new WebUI;