Make alert messages application modal and not window modal,

so assertions cannot be interrupted by terminating the application

Source/Core/DolphinQt/Main.cpp

@@ -39,7 +39,7 @@ static bool QtMsgAlertHandler(const char* caption, const char* text, bool yes_no
                               Common::MsgType style)
 {
   std::optional<bool> r = RunOnObject(QApplication::instance(), [&] {
-    ModalMessageBox message_box(QApplication::activeWindow());
+    ModalMessageBox message_box(QApplication::activeWindow(), Qt::ApplicationModal);
     message_box.setWindowTitle(QString::fromUtf8(caption));
     message_box.setText(QString::fromUtf8(text));