sheetviewer: fix saved fullscreen makes topbar vanish

lib/sheet_viewer_page.dart

@@ -44,6 +44,10 @@ class _SheetViewerPageState extends State<SheetViewerPage>
   @override
   void initState() {
     FullScreen.addListener(this);
+
+    // Load saved fullscreen
+    FullScreen.setFullScreen(widget.config.fullscreen);
+
     super.initState();
     documentLoaded = loadPdf();
   }