[metacity] theme-gtk: suppress logically dead code defect

[Alberts Muktupāvels <muktupavels src gnome org>]

commit e7035b29a856858b85c63b3c35ba2a8040565b02
Author: Alberts Muktupāvels <alberts muktupavels gmail com>
Date:   Mon Mar 15 00:00:08 2021 +0200

    theme-gtk: suppress logically dead code defect
    
    Coverity CID: #1445648

 libmetacity/meta-theme-gtk.c | 2 ++
 1 file changed, 2 insertions(+)
---
diff --git a/libmetacity/meta-theme-gtk.c b/libmetacity/meta-theme-gtk.c
index 80939a19e..13df05712 100644
--- a/libmetacity/meta-theme-gtk.c
+++ b/libmetacity/meta-theme-gtk.c
@@ -953,9 +953,11 @@ meta_theme_gtk_init (MetaThemeGtk *gtk)
             style->layout->hide_buttons = TRUE;
             break;
 
+          /* coverity[dead_error_condition] */
           case META_FRAME_TYPE_LAST:
           default:
             g_assert_not_reached ();
+            break;
         }
 
       gtk->styles[type] = style;