[pitivi] medialibrary: Avoid showing the menu when there are no assets

[Alexandru Băluț <alexbalut src gnome org>]

commit 6462c9deeb885f53e8b99fc98e0762df3b17ab81
Author: Alexandru Băluț <alexandru balut gmail com>
Date:   Tue Jul 5 16:11:05 2016 +0200

    medialibrary: Avoid showing the menu when there are no assets
    
    Differential Revision: https://phabricator.freedesktop.org/D1155

 pitivi/medialibrary.py |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)
---
diff --git a/pitivi/medialibrary.py b/pitivi/medialibrary.py
index b070e1d..0f93c80 100644
--- a/pitivi/medialibrary.py
+++ b/pitivi/medialibrary.py
@@ -1217,6 +1217,9 @@ class MediaLibraryWidget(Gtk.Box, Loggable):
             return None, None
 
         assets = self.getSelectedAssets()
+        if not assets:
+            return None, None
+
         action_group = Gio.SimpleActionGroup()
         menu_model = Gio.Menu()