[longomatch] Fix MediaFileSet Preview getter

[Andoni Morales Alastruey <amorales src gnome org>]

commit 07740ab5dff59007e9560e8c53fb352d4e7bf637
Author: Andoni Morales Alastruey <ylatuya gmail com>
Date:   Mon Mar 2 17:54:23 2015 +0100

    Fix MediaFileSet Preview getter

 LongoMatch.Core/Store/MediaFileSet.cs |    6 +++++-
 1 files changed, 5 insertions(+), 1 deletions(-)
---
diff --git a/LongoMatch.Core/Store/MediaFileSet.cs b/LongoMatch.Core/Store/MediaFileSet.cs
index 7e55c35..31773eb 100644
--- a/LongoMatch.Core/Store/MediaFileSet.cs
+++ b/LongoMatch.Core/Store/MediaFileSet.cs
@@ -45,7 +45,11 @@ namespace LongoMatch.Core.Store
 
                public Image Preview {
                        get {
-                               return Files[MediaFileAngle.Angle1].Preview;
+                               if (Files.Count == 0) {
+                                       return null;
+                               } else {
+                                       return Files[MediaFileAngle.Angle1].Preview;
+                               }
                        }
                }