404/403 pages: Form submit hangs and empty path is stored

On 404/403 pages, Feedback's throbber is displayed infinitely. However, upon reload of the page, the feedback message was stored. However, without path.

This is because 404/403 pages are short-circuited in Drupal. $_GET['q'] is empty, we need to conditionally store $_REQUEST['q'] in such cases.

Additionally, the form action needs to point to a page that does not return a 404/403 (which causes the submission to hang).