[f-spot] Add two more missing disposes.

[Ruben Vermeersch <rubenv src gnome org>]

commit 1df967e8f05531ac3904400c965b09f263a048f6
Author: Ruben Vermeersch <ruben savanne be>
Date:   Thu May 20 14:19:28 2010 +0200

    Add two more missing disposes.

 src/Widgets/SlideShow.cs |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/src/Widgets/SlideShow.cs b/src/Widgets/SlideShow.cs
index 5225c68..b77259d 100644
--- a/src/Widgets/SlideShow.cs
+++ b/src/Widgets/SlideShow.cs
@@ -157,9 +157,9 @@ namespace FSpot.Widgets
 		}
 		protected override void OnDestroyed ()
 		{
-			if (prev != null)
+			if (prev != null && prev != PixbufUtils.ErrorPixbuf)
 				prev.Dispose ();
-			if (next != null)
+			if (next != null && next != PixbufUtils.ErrorPixbuf)
 				next.Dispose ();
 
 			base.OnDestroyed ();