Calling `quirks::set_port()` with invalid prefix characters unset the port (WPT non-compliance)

[hansl]

In browsers (tested on Chrome, Firefox and Safari), doing the following:

const u = new URL("https://example.com:8000");
u.port = "\u00009000";
console.log(u.port);

will show port 8000 (unchanged). This is also tested in the WPT suite here: https://github.com/web-platform-tests/wpt/blob/2a64dae4641fbd61bd4257df460e188f425b492e/url/url-setters-stripping.any.js#L85-L91. That's how the bug came to my attention.

Doing the same using:

let mut url = url::Url::parse("http://example.com:8000").unwrap();
url::quirks::set_port(&mut url, "\u{0000}9000").unwrap();
assert_eq!(url.port(), Some(8000));

will panic with url.port() returning None.