[gnome-applets/wip/muktupavels/werror] brightness: fix -Wswitch-default warning

[Alberts Muktupāvels <muktupavels src gnome org>]

commit 63f71259f673289ac2d96228e3c22d27440b92bd
Author: Alberts Muktupāvels <alberts muktupavels gmail com>
Date:   Sat Apr 4 21:11:23 2020 +0300

    brightness: fix -Wswitch-default warning

 gnome-applets/brightness/brightness-applet.c | 4 ++++
 1 file changed, 4 insertions(+)
---
diff --git a/gnome-applets/brightness/brightness-applet.c b/gnome-applets/brightness/brightness-applet.c
index 76a836de1..9dcbc062c 100644
--- a/gnome-applets/brightness/brightness-applet.c
+++ b/gnome-applets/brightness/brightness-applet.c
@@ -123,6 +123,10 @@ gpm_applet_size_allocate_cb (GtkWidget    *widget,
                case GTK_ORIENTATION_HORIZONTAL:
                        size = allocation->height;
                        break;
+
+               default:
+                       g_assert_not_reached ();
+                       break;
        }
 
        /* copied from button-widget.c in the panel */