[gnome-tweak-tool/gnome-3-26] appearance: Don't duplicate the theme name

[Jeremy Bicha <jbicha src gnome org>]

commit 9349e9b3a3b9410ebb60edf9f2e5beccabb40275
Author: Jeremy Bicha <jbicha ubuntu com>
Date:   Fri Nov 3 14:41:30 2017 -0400

    appearance: Don't duplicate the theme name
    
    A theme name should not be listed more than once
    
    https://bugzilla.gnome.org/show_bug.cgi?id=762789

 gtweak/tweaks/tweak_group_appearance.py |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/gtweak/tweaks/tweak_group_appearance.py b/gtweak/tweaks/tweak_group_appearance.py
index 67bada6..483d028 100644
--- a/gtweak/tweaks/tweak_group_appearance.py
+++ b/gtweak/tweaks/tweak_group_appearance.py
@@ -56,7 +56,7 @@ class GtkThemeSwitcher(GSettingsComboTweak):
         valid = walk_directories(dirs, lambda d:
                     os.path.exists(os.path.join(d, "gtk-3.0", "gtk.css")) or \
                          os.path.exists(os.path.join(d, "gtk-3.{}".format(gtk_ver))))
-        return valid
+        return set(valid)
 
 class IconThemeSwitcher(GSettingsComboTweak):
     def __init__(self, **options):
@@ -74,7 +74,7 @@ class IconThemeSwitcher(GSettingsComboTweak):
         valid = walk_directories(dirs, lambda d:
                     os.path.isdir(d) and \
                        os.path.exists(os.path.join(d, "index.theme")))
-        return valid
+        return set(valid)
 
 class CursorThemeSwitcher(GSettingsComboTweak):
     def __init__(self, **options):