[gimp] app: fix list leak, as reported by Massimo.

[Jehan <jehanp src gnome org>]

commit b1afc3397189a0f456c9aea1a54660e06a877891
Author: Jehan <jehan girinstud io>
Date:   Sat Aug 14 19:02:29 2021 +0200

    app: fix list leak, as reported by Massimo.

 app/widgets/gimpdnd.c | 1 +
 1 file changed, 1 insertion(+)
---
diff --git a/app/widgets/gimpdnd.c b/app/widgets/gimpdnd.c
index fda5a89953..0c1991e9ed 100644
--- a/app/widgets/gimpdnd.c
+++ b/app/widgets/gimpdnd.c
@@ -2206,6 +2206,7 @@ gimp_dnd_get_viewable_list_icon (GtkWidget      *widget,
       desc = gimp_viewable_get_description (viewable, NULL);
       desc_width_chars =  MIN (strlen (desc), 10);
     }
+  g_list_free (viewables);
 
   if (desc)
     {