[mutter] compositor: Only disconnect/connect top-window signals if it changed

[Marco Trevisan <marcotrevi src gnome org>]

commit 7645c51c5408678e2b48ac61efefcbdf5a24b6ee
Author: Marco Trevisan (Treviño) <mail 3v1n0 net>
Date:   Thu Jun 13 10:37:28 2019 +0200

    compositor: Only disconnect/connect top-window signals if it changed
    
    If the stack changed but the top window didn't, there's no need to disconnect
    the signal and connect it again.
    
    https://gitlab.gnome.org/GNOME/mutter/merge_requests/660

 src/compositor/compositor.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)
---
diff --git a/src/compositor/compositor.c b/src/compositor/compositor.c
index d6c9f90f1..95a1de8ea 100644
--- a/src/compositor/compositor.c
+++ b/src/compositor/compositor.c
@@ -1034,6 +1034,7 @@ void
 meta_compositor_sync_stack (MetaCompositor  *compositor,
                             GList           *stack)
 {
+  MetaWindowActor *top_window_actor;
   GList *old_stack;
 
   /* This is painful because hidden windows that we are in the process
@@ -1117,12 +1118,17 @@ meta_compositor_sync_stack (MetaCompositor  *compositor,
 
   sync_actor_stacking (compositor);
 
+  top_window_actor = get_top_visible_window_actor (compositor);
+
+  if (compositor->top_window_actor == top_window_actor)
+    return;
+
   if (compositor->top_window_actor)
     g_signal_handlers_disconnect_by_func (compositor->top_window_actor,
                                           on_top_window_actor_destroyed,
                                           compositor);
 
-  compositor->top_window_actor = get_top_visible_window_actor (compositor);
+  compositor->top_window_actor = top_window_actor;
 
   if (compositor->top_window_actor)
     g_signal_connect (compositor->top_window_actor, "destroy",