Code style fix.

--HG--
branch : develop

src/app/mainwindow.h

@@ -52,7 +52,7 @@ class MainWindow : public QMainWindow
     Q_OBJECT
 public:
     explicit MainWindow(QWidget *parent = nullptr);
-    ~MainWindow();
+    virtual ~MainWindow();
     void               LoadPattern(const QString &curFile);
 public slots:
     void               mouseMove(const QPointF &scenePos);