[gnome-tweak-tool/gnome-3-24] extensions: Bail out early when not running under GNOME

[Jeremy Bicha <jbicha src gnome org>]

commit d3ddfac1815362cc713432bd26ba384d012fe9e0
Author: Jeremy Bicha <jbicha ubuntu com>
Date:   Sun Jun 11 20:58:12 2017 -0400

    extensions: Bail out early when not running under GNOME
    
    GNOME Shell extensions aren't useful in non-GNOME environments,
    so return right after initializing the empty tweak group to make
    sure it is kept hidden in that case.
    
    This commit also fixes a 3.24 regression that caused
    GNOME Tweak Tool to not start if GNOME Shell wasn't running
    
    https://bugzilla.gnome.org/show_bug.cgi?id=780794
    https://bugzilla.gnome.org/show_bug.cgi?id=783563

 gtweak/tweaks/tweak_group_shell_extensions.py |    5 ++++-
 1 files changed, 4 insertions(+), 1 deletions(-)
---
diff --git a/gtweak/tweaks/tweak_group_shell_extensions.py b/gtweak/tweaks/tweak_group_shell_extensions.py
index 8ff6cd1..a42db1f 100644
--- a/gtweak/tweaks/tweak_group_shell_extensions.py
+++ b/gtweak/tweaks/tweak_group_shell_extensions.py
@@ -304,7 +304,10 @@ class ShellExtensionTweakGroup(ListBoxTweakGroup):
         ListBoxTweakGroup.__init__(self,
                                    _("Extensions"),
                                    *extension_tweaks)
-        
+
+        if shell is None:
+            return # We're done
+
         self.titlebar_widget = Gtk.Switch(visible=True)
         shell._settings.bind("disable-user-extensions", self.titlebar_widget,
                              "active", Gio.SettingsBindFlags.INVERT_BOOLEAN)