fix: better handle Windows shutting down in newer Qt versions (#6368)

src/widgets/Window.cpp

@@ -153,10 +153,19 @@ bool Window::event(QEvent *event)
 
 void Window::closeEvent(QCloseEvent *)
 {
+    if (isAppAboutToQuit())
+    {
+        qCWarning(chatterinoWidget)
+            << "Window closeEvent ran when Application is already dead";
+        return;
+    }
+
+    auto *app = getApp();
+
     if (this->type_ == WindowType::Main)
     {
-        getApp()->getWindows()->save();
-        getApp()->getWindows()->closeAll();
+        app->getWindows()->save();
+        app->getWindows()->closeAll();
     }
     else
     {
@@ -167,7 +176,7 @@ void Window::closeEvent(QCloseEvent *)
     // Ensure selectedWindow_ is never an invalid pointer.
     // WindowManager will return the main window if no window is pointed to by
     // `selectedWindow_`.
-    getApp()->getWindows()->selectedWindow_ = nullptr;
+    app->getWindows()->selectedWindow_ = nullptr;
 
     this->closed.invoke();