[gimp] app: fix crash when deleting channel

[Thomas Manni <tmanni src gnome org>]

commit b8abac1777c55ef1680e0b9b28ad8e64edb15097
Author: Thomas Manni <thomas manni free fr>
Date:   Sun Jan 31 10:16:59 2021 +0100

    app: fix crash when deleting channel

 app/core/gimpimage.c | 3 +++
 1 file changed, 3 insertions(+)
---
diff --git a/app/core/gimpimage.c b/app/core/gimpimage.c
index 7ac19ebbdf..604cb49d25 100644
--- a/app/core/gimpimage.c
+++ b/app/core/gimpimage.c
@@ -5358,6 +5358,7 @@ gimp_image_remove_channel (GimpImage   *image,
   private = GIMP_IMAGE_GET_PRIVATE (image);
 
   selected_channels = gimp_image_get_selected_channels (image);
+  selected_channels = g_list_copy (selected_channels);
 
   if (push_undo)
     gimp_image_undo_push_channel_remove (image, C_("undo-type", "Remove Channel"), channel,
@@ -5382,6 +5383,8 @@ gimp_image_remove_channel (GimpImage   *image,
         gimp_image_unset_selected_channels (image);
     }
 
+  g_list_free (selected_channels);
+
   gimp_item_end_move (GIMP_ITEM (channel), push_undo);
 
   g_object_unref (channel);