Redraw RootCanvasWidget on Resize

React properly when the widget is resized...

src/rootcanvaswidget.cpp

@@ -78,6 +78,8 @@ void RootCanvasWidget::resizeEvent(QResizeEvent* const event)
             static_cast<UInt_t>(event->size().width()),
             static_cast<UInt_t>(event->size().height())
         );
+        _canvas->Draw();
+        _canvas->Modified();
         _canvas->Resize();
         _canvas->Update();
     }