[pitivi] mainwindow: Fix how we enable the undo button

[Thibault Saunier <tsaunier src gnome org>]

commit 7443fe174a3b6b04222ad563d257bfc01b1976dc
Author: Thibault Saunier <tsaunier gnome org>
Date:   Fri Apr 1 12:18:11 2016 +0200

    mainwindow: Fix how we enable the undo button
    
    Taking into account the undo state to enable it or not

 pitivi/application.py |    4 +++-
 1 files changed, 3 insertions(+), 1 deletions(-)
---
diff --git a/pitivi/application.py b/pitivi/application.py
index c89f0d9..0f7b978 100644
--- a/pitivi/application.py
+++ b/pitivi/application.py
@@ -363,9 +363,11 @@ class Pitivi(Gtk.Application, Loggable):
         self._syncDoUndo(action_log)
 
     def _syncDoUndo(self, action_log):
-        can_undo = bool(action_log.undo_stacks)
         # TODO: Remove this once we revisit undo/redo T3360
         can_undo = in_devel()
+
+        if can_undo:
+            can_undo = bool(action_log.undo_stacks)
         self.undo_action.set_enabled(can_undo)
 
         can_redo = bool(action_log.redo_stacks)