Handle // scheme prefix

[acrosman]

Fixes #74

During media download, if the scheme is expressed as // replaces with the current URL's scheme before proceeding through the process.

[ashishb]

Thanks for the contribution.
Please point me to some official documentation of /// scheme.

[acrosman]

It's commonly known as protocol relative URL, the // are formally knows as a network-path reference : https://datatracker.ietf.org/doc/html/rfc3986#section-4.2

A relative reference that begins with two slash characters is termed
a network-path reference; such references are rarely used. A
relative reference that begins with a single slash character is
termed an absolute-path reference.

My sample file contained a generated link that somehow has three / instead of two, which threw me off. I'll update the text above and PR in a few minutes.