Make alert messages application modal and not window modal,

so assertions cannot be interrupted by terminating the application

Source/Core/DolphinQt/QtUtils/ModalMessageBox.h

@@ -10,7 +10,7 @@
 class ModalMessageBox : public QMessageBox
 {
 public:
-  explicit ModalMessageBox(QWidget* parent);
+  explicit ModalMessageBox(QWidget* parent, Qt::WindowModality modality = Qt::WindowModal);
 
   static int critical(QWidget* parent, const QString& title, const QString& text,
                       StandardButtons buttons = Ok, StandardButton default_button = NoButton);