[pitivi] render: Show unsupported only when needed

[Alexandru Băluț <alexbalut src gnome org>]

commit 7b1f737373e21df6108698c1e400b9d568c1a04e
Author: Alexandru Băluț <alexandru balut gmail com>
Date:   Wed Oct 25 22:15:05 2017 +0200

    render: Show unsupported only when needed
    
    Fixes T7736
    
    Reviewed-by: Thibault Saunier <tsaunier gnome org>
    Differential Revision: https://phabricator.freedesktop.org/D1867

 pitivi/render.py |   15 ++++++++-------
 1 files changed, 8 insertions(+), 7 deletions(-)
---
diff --git a/pitivi/render.py b/pitivi/render.py
index 1f791b8..b97879d 100644
--- a/pitivi/render.py
+++ b/pitivi/render.py
@@ -638,13 +638,14 @@ class RenderDialog(Loggable):
         for row in data_supported:
             model.append(None, row)
 
-        # Translators: This item appears in a combobox's popup and
-        # contains as children the unsupported (but still available)
-        # muxers and encoders.
-        unsupported_iter = model.append(None, (_("Unsupported"), None))
-        data_unsupported.sort()
-        for row in data_unsupported:
-            model.append(unsupported_iter, row)
+        if data_unsupported:
+            # Translators: This item appears in a combobox's popup and
+            # contains as children the unsupported (but still available)
+            # muxers and encoders.
+            unsupported_iter = model.append(None, (_("Unsupported"), None))
+            data_unsupported.sort()
+            for row in data_unsupported:
+                model.append(unsupported_iter, row)
 
         return model