Deleting a node displayed by Panels forces redirect to the same node resulting in a 404

If the "Edit node" link that is added by plugins/content_types/node/node.inc is used to eventually delete a node, the browser will end up at a 404 page at the end because it is being redirected back to the page it just deleted. This happens because CTools unconditionally sets the destination= query string for that link, which is inconsistent with the standard behaviors of the node module. The attached patch corrects this behavior by only setting the query parameter if $_REQUEST['destination'] is set, similar to how node_form_delete_submit() works in node.pages.inc.