[beast: 7/8] GXK: widget_lower_windows: fix invalid GdkWindow child list modifications

[Tim Janik <timj src gnome org>]

commit 74a70adeb7c5d30c993df69ca804e27b51c1312b
Author: Tim Janik <timj gnu org>
Date:   Tue Sep 22 00:43:24 2015 +0200

    GXK: widget_lower_windows: fix invalid GdkWindow child list modifications
    
    While iterating over a window's child list, the code used to modify the
    very list by calling gdk_window_lower(). This could lead to occasional
    crashes or assertion warnings.

 beast-gtk/gxk/gxkauxwidgets.cc |   15 ++++++++++-----
 1 files changed, 10 insertions(+), 5 deletions(-)
---
diff --git a/beast-gtk/gxk/gxkauxwidgets.cc b/beast-gtk/gxk/gxkauxwidgets.cc
index 4948a5d..e82b1fa 100644
--- a/beast-gtk/gxk/gxkauxwidgets.cc
+++ b/beast-gtk/gxk/gxkauxwidgets.cc
@@ -503,14 +503,19 @@ widget_mute_events (GtkWidget *widget,
 static void
 widget_lower_windows (GtkWidget *widget)
 {
-  GList *list = gdk_window_peek_children (widget->window);
-  for (; list; list = list->next)
+  std::vector<GdkWindow*> wins;
+  // gdk_window_peek_children's result is modified by gdk_window_lower
+  for (GList *list = gdk_window_peek_children (widget->window); list; list = list->next)
     {
-      gpointer user_data;
-      gdk_window_get_user_data ((GdkWindow*) list->data, &user_data);
+      GdkWindow *win = (GdkWindow*) list->data;
+      gpointer user_data = NULL;
+      gdk_window_get_user_data (win, &user_data);
       if (user_data == (gpointer) widget)
-        gdk_window_lower ((GdkWindow*) list->data);
+        wins.push_back (win);
     }
+  // so here we walk the list of windows that need lowering
+  for (GdkWindow *win : wins)
+    gdk_window_lower (win);
 }
 static void
 widget_hide_insensitive (GtkWidget *widget)