[pitivi] dialogs: Fix the preferences dialog

[Alexandru Băluț <alexbalut src gnome org>]

commit 468550ead67ccd12d3951a0ff5b3abd40313cccc
Author: Alexandru Băluț <alexandru balut gmail com>
Date:   Thu Oct 12 00:24:37 2017 +0200

    dialogs: Fix the preferences dialog
    
    Broken in 4f9f0b0795cb77488e26bef7a5b28c80836b91f7
    
    Fixes T7845

 pitivi/dialogs/prefs.py |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/pitivi/dialogs/prefs.py b/pitivi/dialogs/prefs.py
index 6f78983..9635535 100644
--- a/pitivi/dialogs/prefs.py
+++ b/pitivi/dialogs/prefs.py
@@ -234,7 +234,7 @@ class PreferencesDialog(Loggable):
             self.widgets[attrname] = widget
             # Add a semicolon, except for checkbuttons.
             if isinstance(widget, widgets.ToggleWidget):
-                widget.set_label(label)
+                widget.check_button.set_label(label)
                 label_widget = None
             else:
                 # Translators: This adds a semicolon to an already