[gimp] app: fix one more ugly leak.

[Jehan <jehanp src gnome org>]

commit 2d1d2340dbed3a16552700c1983418bff12fc227
Author: Jehan <jehan girinstud io>
Date:   Sun Aug 15 01:44:46 2021 +0200

    app: fix one more ugly leak.
    
    This one was definitely tricky. Thanks again to Massimo for catching it!

 app/widgets/gimpitemtreeview.c | 23 ++++++++++++++++++-----
 1 file changed, 18 insertions(+), 5 deletions(-)
---
diff --git a/app/widgets/gimpitemtreeview.c b/app/widgets/gimpitemtreeview.c
index 81c953be7d..5f163db569 100644
--- a/app/widgets/gimpitemtreeview.c
+++ b/app/widgets/gimpitemtreeview.c
@@ -1254,11 +1254,12 @@ gimp_item_tree_view_drop_viewables (GimpContainerTreeView   *tree_view,
                                     GtkTreeViewDropPosition  drop_pos)
 {
   GimpItemTreeViewClass *item_view_class;
-  GimpItemTreeView      *item_view         = GIMP_ITEM_TREE_VIEW (tree_view);
+  GimpItemTreeView      *item_view              = GIMP_ITEM_TREE_VIEW (tree_view);
   GList                 *iter;
-  GimpImage             *src_image         = NULL;
-  GType                  src_viewable_type = G_TYPE_NONE;
-  gint                   dest_index        = -1;
+  GimpImage             *src_image              = NULL;
+  GType                  src_viewable_type      = G_TYPE_NONE;
+  gint                   dest_index             = -1;
+  gboolean               src_viewables_reversed = FALSE;
 
   g_return_if_fail (g_list_length (src_viewables) > 0);
 
@@ -1297,7 +1298,10 @@ gimp_item_tree_view_drop_viewables (GimpContainerTreeView   *tree_view,
       (drop_pos == GTK_TREE_VIEW_DROP_INTO_OR_AFTER &&
        dest_viewable                                &&
        gimp_viewable_get_children (dest_viewable)))
-    src_viewables = g_list_reverse (src_viewables);
+    {
+      src_viewables_reversed = TRUE;
+      src_viewables = g_list_reverse (src_viewables);
+    }
 
   if (item_view->priv->image != src_image ||
       ! g_type_is_a (src_viewable_type, item_view_class->item_type))
@@ -1365,6 +1369,15 @@ gimp_item_tree_view_drop_viewables (GimpContainerTreeView   *tree_view,
         }
     }
 
+  if (src_viewables_reversed)
+    /* The caller keeps a copy to src_viewables to free it. If we
+     * reverse it, the pointer stays valid yet ends up pointing to the
+     * now last (previously first) element of the list. So we leak the
+     * whole list but this element. Let's reverse back the list to have
+     * next and prev pointers same as call time.
+     */
+    src_viewables = g_list_reverse (src_viewables);
+
   gimp_image_undo_group_end (item_view->priv->image);
   gimp_image_flush (item_view->priv->image);
 }