libfetch: parse scheme://domain:/ correctly

[khng]

Summary

This improves URL-parsing compability with cURL, and unbreaks parsing of
similar kinds of URLs after commit 8d9de5b10a24.

Sponsored by: Juniper Networks, Inc.

[des]

Can you please provide an example of a URL which is parsed incorrectly without this patch?

[khng]

@des something like https://example.com:/ used to work before https://reviews.freebsd.org/rG8d9de5b10a24bd2d79ed99f139c0ac28c09b15ca. Meanwhile, curl -L https://example.com:/ gives the HTML page just as curl -L https://example.com/, and is true for Firefox and Chromium-based browsers as well.