Destroy desktop integration at correct place

Otherwise it is destructed in QObject destructor, i.e. after GUI application is already destructed.
This can be related to some problems with system tray icon.

PR #18108.
Closes #18093.

src/app/application.cpp

@@ -706,7 +706,7 @@ try
 #ifndef DISABLE_GUI
     UIThemeManager::initInstance();
 
-    m_desktopIntegration = new DesktopIntegration(this);
+    m_desktopIntegration = new DesktopIntegration;
     m_desktopIntegration->setToolTip(tr("Loading torrents..."));
 #ifndef Q_OS_MACOS
     auto *desktopIntegrationMenu = new QMenu;
@@ -1201,6 +1201,7 @@ void Application::cleanup()
         ::ShutdownBlockReasonDestroy(reinterpret_cast<HWND>(m_window->effectiveWinId()));
 #endif // Q_OS_WIN
         delete m_window;
+        delete m_desktopIntegration;
         UIThemeManager::freeInstance();
     }
 #endif // DISABLE_GUI