add_rewrite_endpoint does not work for attachments

[Curioso]

The functionality for adding endpoints in rewrite rules does not work for attachments.
In wp-includes/rewrite.php:

                    //do endpoints for attachments
                    if ($endpoint) { foreach ($ep_query_append as $regex => $ep) {
                        if ($ep[0] & EP_ATTACHMENT) {
                            $rewrite[$sub1 . $regex] = $subquery . '?' . $ep[1] . $this->preg_index(2);
                            $rewrite[$sub2 . $regex] = $subquery . '?' . $ep[1] . $this->preg_index(2);
                        }
                    } }                                                                                              

should be:

                    //do endpoints for attachments
                    if ($endpoints) { foreach ($ep_query_append as $regex => $ep) {
                        if ($ep[0] & EP_ATTACHMENT) {
                            $rewrite[$sub1 . $regex] = $subquery . $ep[1] . $this->preg_index(2);
                            $rewrite[$sub2 . $regex] = $subquery . $ep[1] . $this->preg_index(2);
                        }
                    } }                                                                                              

Note the typing error in $endpoints, and the '?' is already present in $subquery.

created diff based on code in Description. untested.

see also: #9477. same bug, with a plugin to test

broken patch

see also: #5553 (#9477 was a dupe)

(In [12271]) Fix attachment rewrite endpoints. Props Curioso. fixes #5553