[metacity] frames: suppress logically dead code defect

[Alberts Muktupāvels <muktupavels src gnome org>]

commit 6210cf9018d970dd559ca1834d03f694cb504014
Author: Alberts Muktupāvels <alberts muktupavels gmail com>
Date:   Sun Mar 14 20:15:36 2021 +0200

    frames: suppress logically dead code defect
    
    META_GRAB_OP_NONE enumeration value is intentionally added here
    to avoid compiler warning about unhandled value.
    
    Coverity CID: #1445650

 src/ui/frames.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)
---
diff --git a/src/ui/frames.c b/src/ui/frames.c
index 35237cd4c..e47046f02 100644
--- a/src/ui/frames.c
+++ b/src/ui/frames.c
@@ -1903,7 +1903,6 @@ meta_frames_button_release_event    (GtkWidget           *widget,
           meta_core_end_grab_op (frames->xdisplay, event->time);
           break;
 
-        case META_GRAB_OP_NONE:
         case META_GRAB_OP_MOVING:
         case META_GRAB_OP_RESIZING_SE:
         case META_GRAB_OP_RESIZING_S:
@@ -1932,6 +1931,11 @@ meta_frames_button_release_event    (GtkWidget           *widget,
         case META_GRAB_OP_KEYBOARD_WORKSPACE_SWITCHING:
           break;
 
+        /* coverity[dead_error_line] */
+        case META_GRAB_OP_NONE:
+          g_assert_not_reached ();
+          break;
+
         default:
           break;
         }