Eli Zaretskii <eliz@gnu.org> writes:

>> If it is a full windows path, we DO want to turn that into a file url.
>> 
>> So how do we detect that is is a windows path, and not a URL already?
>
> You test that system-type is windows-nt AND that the
> file-name-absolute-p returns non-nil for the argument.

That is incredible simple. Maybe something like this patch will work: