compdfkit(win) - fix 显示设置

Demo/Examples/PDFViewer/MainPage.xaml.cs

@@ -1136,6 +1136,7 @@ namespace PDFViewer
             {
                 if (ViewSettingBtn.IsChecked == true)
                 {
+                    displayPanel = new CPDFDisplaySettingsControl();
                     displayPanel.InitWithPDFViewer(pdfViewControl.PDFView);
                     PropertyContainer.Child = displayPanel;
                     PropertyContainer.Visibility = Visibility.Visible;