title: Javafx-snapshot of scene doesnt show values and series
body: <p>I made a really short app, which uses javafx to generate a chart. App shows the right values(chart) but when I do snapshot, image shows just an axis and labels, but not the series and values.</p>
  
  <pre><code>    stage.setTitle("Line Chart Sample");        
      final DateAxis xAxis = new DateAxis();
      final NumberAxis yAxis = new NumberAxis();
  
      xAxis.setLabel("Number of Month");
      yAxis.setLabel("Count");
      final LineChart&lt;Date, Number&gt; lineChart =  new LineChart&lt;&gt;(xAxis,yAxis);       
      Scene scene  = new Scene(lineChart,1000,700);
  
      lineChart.setTitle("Stock Monitoring, 2010");
      XYChart.Series series = new XYChart.Series();
      series.setName("My portfolio");
  
      series.getData().add(new XYChart.Data(new GregorianCalendar(2012, 11, 15).getTime(), 23));
      series.getData().add(new XYChart.Data(new GregorianCalendar(2012, 11, 16).getTime(), 14));
      series.getData().add(new XYChart.Data(new GregorianCalendar(2012, 11, 17).getTime(), 15));
      series.getData().add(new XYChart.Data(new GregorianCalendar(2012, 11, 18).getTime(), 24));
      series.getData().add(new XYChart.Data(new GregorianCalendar(2012, 11, 19).getTime(), 34));
      series.getData().add(new XYChart.Data(new GregorianCalendar(2012, 11, 20).getTime(), 36));
      series.getData().add(new XYChart.Data(new GregorianCalendar(2012, 11, 21).getTime(), 22));
      lineChart.getData().add(series);        
      stage.setScene(scene);
      stage.show();
      WritableImage img = new WritableImage(1000, 700); 
      File file = new File("saved.png");      
      scene.snapshot(img);        
      RenderedImage renderedImage = SwingFXUtils.fromFXImage(img, null);        
      ImageIO.write(renderedImage,"png", file);      
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/1nIUV.png" rel="nofollow noreferrer">here is a saved file</a></p>
  
  <p><a href="https://i.stack.imgur.com/gfkmW.png" rel="nofollow noreferrer">here is a screenshot from app</a></p>
  
  <p>I have no idea what I am doing wrong.</p>