Suppress compiler warnings

QuickLook.Plugin/QuickLook.Plugin.VideoViewer/ViewerPanel.xaml.cs

@@ -12,12 +12,14 @@ namespace QuickLook.Plugin.VideoViewer
     /// </summary>
     public partial class ViewerPanel : UserControl, IDisposable
     {
-        private ContextObject _context;
+        private readonly ContextObject _context;
 
         public ViewerPanel(ContextObject context)
         {
             InitializeComponent();
 
+            _context = context;
+
             buttonPlayPause.MouseLeftButtonUp += TogglePlayPause;
 
             mediaElement.PropertyChanged += ChangePlayPauseButton;