[banshee/stable-1.8] [Services] Prevent NRE caused in DatabaseTrackInfo.Update()

[Gabriel Burt <gburt src gnome org>]

commit 0fa2ede6990b12dbcf6ee83e05601b6d968b472f
Author: Andrés G. Aragoneses <knocte gmail com>
Date:   Tue Oct 5 03:49:43 2010 +0200

    [Services] Prevent NRE caused in DatabaseTrackInfo.Update()
    
    The infrastructure commit for bgo#589196 unfortunately caused bgo#631277

 .../DatabaseTrackInfo.cs                           |    4 +++-
 1 files changed, 3 insertions(+), 1 deletions(-)
---
diff --git a/src/Core/Banshee.Services/Banshee.Collection.Database/DatabaseTrackInfo.cs b/src/Core/Banshee.Services/Banshee.Collection.Database/DatabaseTrackInfo.cs
index f83a441..016c1a6 100644
--- a/src/Core/Banshee.Services/Banshee.Collection.Database/DatabaseTrackInfo.cs
+++ b/src/Core/Banshee.Services/Banshee.Collection.Database/DatabaseTrackInfo.cs
@@ -170,7 +170,9 @@ namespace Banshee.Collection.Database
 
         public override void Update ()
         {
-            PrimarySource.UpdateMetadata (this);
+            if (PrimarySource != null) {
+                PrimarySource.UpdateMetadata (this);
+            }
             base.Update ();
         }