[pitivi] Fix double clicking in the source list. Fixes #589807.

[Edward Hervey <edwardrv src gnome org>]

commit bbd1683a7c148e202df50c7dd03b3ad0db0b0fa5
Author: Alessandro Decina <alessandro d gmail com>
Date:   Mon Jul 27 12:55:01 2009 +0200

    Fix double clicking in the source list. Fixes #589807.
    
    Double clicking was broken in 6f623e01, which fixed #572327. Hopefully I didn't
    break it again.

 pitivi/ui/sourcelist.py |    5 ++++-
 1 files changed, 4 insertions(+), 1 deletions(-)
---
diff --git a/pitivi/ui/sourcelist.py b/pitivi/ui/sourcelist.py
index eef3a9c..7b8e487 100644
--- a/pitivi/ui/sourcelist.py
+++ b/pitivi/ui/sourcelist.py
@@ -585,7 +585,10 @@ class SourceList(gtk.VBox, Loggable):
         result = treeview.get_path_at_pos(int(event.x), int(event.y))
         if result:
             path = result[0]
-            return treeview.get_selection().path_is_selected(path)
+            selection = treeview.get_selection()
+
+            return selection.path_is_selected(path) and selection.count_selected_rows() > 1
+
         return False
 
     def _nothingUnderMouse(self, treeview, event):