[pitivi] ui: Make sure to use the sorted streams list

[Alexandru Băluț <alexbalut src gnome org>]

commit fbcae35cf618d3bd92288c97ab49b59eb90a5be2
Author: Alexandru Băluț <alexandru balut gmail com>
Date:   Wed Dec 21 14:19:04 2016 +0100

    ui: Make sure to use the sorted streams list
    
    Reviewed-by: Thibault Saunier <tsaunier gnome org>
    Differential Revision: https://phabricator.freedesktop.org/D1570

 pitivi/utils/ui.py |    5 +++--
 1 files changed, 3 insertions(+), 2 deletions(-)
---
diff --git a/pitivi/utils/ui.py b/pitivi/utils/ui.py
index ea83ae2..3df3d01 100644
--- a/pitivi/utils/ui.py
+++ b/pitivi/utils/ui.py
@@ -266,8 +266,9 @@ def beautify_asset(asset):
             return len(ranks)
 
     info = asset.get_info()
-    info.get_stream_list().sort(key=stream_sort_key)
-    for stream in info.get_stream_list():
+    streams = info.get_stream_list()
+    streams.sort(key=stream_sort_key)
+    for stream in streams:
         try:
             beautified_string = beautify_stream(stream)
         except NotImplementedError: