[banshee] GStreamerSharp: fix DVD playback

[Andrés Aragoneses <aaragoneses src gnome org>]

commit 48bf8f23fb10de00380a7a2e7108de63bc6a6a6a
Author: Andrés G. Aragoneses <knocte gmail com>
Date:   Mon Jan 6 18:26:30 2014 +0100

    GStreamerSharp: fix DVD playback
    
    DVD playback was throwing a NullReferenceException because the
    navigation element found by Bin.GetByInterface() couldn't be
    casted directly to INavigation, as NavigationAdapter.GetObject()
    had to be used.

 .../Banshee.GStreamerSharp/DvdManager.cs           |   10 ++++++----
 1 files changed, 6 insertions(+), 4 deletions(-)
---
diff --git a/src/Backends/Banshee.GStreamerSharp/Banshee.GStreamerSharp/DvdManager.cs 
b/src/Backends/Banshee.GStreamerSharp/Banshee.GStreamerSharp/DvdManager.cs
index 3448e05..7237fb2 100644
--- a/src/Backends/Banshee.GStreamerSharp/Banshee.GStreamerSharp/DvdManager.cs
+++ b/src/Backends/Banshee.GStreamerSharp/Banshee.GStreamerSharp/DvdManager.cs
@@ -48,6 +48,9 @@ namespace Banshee.GStreamerSharp
         INavigation Navigation {
             get; set;
         }
+        Element NavigationElement {
+            get; set;
+        }
 
         public string Device {
             get; set;
@@ -144,7 +147,7 @@ namespace Banshee.GStreamerSharp
             if (Navigation == null) {
                 FindNavigation (playbin);
             }
-            if (!(((Element)Navigation).Query (query) && NavigationAdapter.ParseCommands (query, out cmds))) 
{
+            if (!(NavigationElement.Query (query) && NavigationAdapter.ParseCommands (query, out cmds))) {
                 return;
             }
             foreach (NavigationCommand cmd in cmds) {
@@ -178,11 +181,10 @@ namespace Banshee.GStreamerSharp
                 }
             }
 
-            navigation = (video_sink is Bin)
+            NavigationElement = (video_sink is Bin)
                 ? ((Bin)video_sink).GetByInterface (NavigationAdapter.GType)
                 : video_sink;
-
-            Navigation = navigation as INavigation;
+            Navigation = NavigationAdapter.GetObject (navigation);
         }
 
         public void NotifyMouseMove (Element playbin, double x, double y)