[gnome-control-center/gnome-3-34] thunderbolt: Fix GCancellable leak

[Robert Ancell <rancell src gnome org>]

commit 6f7dff8f65a47474b4e4ca3ae2c0f27f360f8317
Author: Robert Ancell <robert ancell canonical com>
Date:   Fri Jan 31 10:06:06 2020 +1300

    thunderbolt: Fix GCancellable leak

 panels/thunderbolt/cc-bolt-panel.c | 1 +
 1 file changed, 1 insertion(+)
---
diff --git a/panels/thunderbolt/cc-bolt-panel.c b/panels/thunderbolt/cc-bolt-panel.c
index 10570e168..fdd8fa02a 100644
--- a/panels/thunderbolt/cc-bolt-panel.c
+++ b/panels/thunderbolt/cc-bolt-panel.c
@@ -900,6 +900,7 @@ cc_bolt_panel_dispose (GObject *object)
 
   /* cancel any ongoing operation */
   g_cancellable_cancel (panel->cancel);
+  g_clear_object (&panel->cancel);
 
   /* Must be destroyed in dispose, not finalize. */
   g_clear_pointer ((GtkWidget **) &panel->device_dialog, gtk_widget_destroy);