[gnome-panel] add-applet-window: fix cast-function-type warning

[Alberts Muktupāvels <muktupavels src gnome org>]

commit 8694e4f90b5697e08a67d5118b94c7b6ba49d9b3
Author: Alberts Muktupāvels <alberts muktupavels gmail com>
Date:   Thu Sep 13 16:13:38 2018 +0300

    add-applet-window: fix cast-function-type warning

 gnome-panel/gp-add-applet-window.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)
---
diff --git a/gnome-panel/gp-add-applet-window.c b/gnome-panel/gp-add-applet-window.c
index 6dd86c937..d802c046d 100644
--- a/gnome-panel/gp-add-applet-window.c
+++ b/gnome-panel/gp-add-applet-window.c
@@ -337,6 +337,13 @@ add_module (GpAddAppletWindow *window,
                               NULL);
 }
 
+static void
+destroy_module_cb (GtkWidget *widget,
+                    gpointer   user_data)
+{
+  gtk_widget_destroy (widget);
+}
+
 static void
 rebuild_modules_list (GpAddAppletWindow *window)
 {
@@ -345,7 +352,7 @@ rebuild_modules_list (GpAddAppletWindow *window)
   GList *children;
 
   modules_box = GTK_CONTAINER (window->modules_box);
-  gtk_container_foreach (modules_box, (GtkCallback) gtk_widget_destroy, NULL);
+  gtk_container_foreach (modules_box, destroy_module_cb, NULL);
 
   modules = gp_module_manager_get_modules (window->module_manager);