It was technically possible to register a link that would loop on itself
by abusing the query and fragment parts of the URL. It was possible to
register a link targetting `#` and get the following HTTP exchange which
enter an infinite loop.
GET /r/bAd HTTP/1.0
HTTP/1.0 301 Redirect
Location: #
GET /r/bAd# HTTP/1.0
Prevent such links from being registered and highlight flaws inside the
`validate_url` method with unittests.
Part-of: odoo/odoo#150678