bug#25183: 26.0.50; expanding quoted file name on w32

[Noam Postavsky <npostavs@users.sourceforge.net>]

>>> (expand-file-name "/:~/path/./file")
>>> => "/:~/path/file"

>>> (expand-file-name "/:~/path/./file")
>>> => "/:c:/Users/lb01177/AppData/Roaming/path/file"

>
> (file-name-absolute-p "/:~/path/./file")
> => t

I think all these cases are user error, `(emacs) Quoted File Names' says

    You can "quote" an absolute file name [...] add ‘/:’ at the beginning

But you cannot quote a relative file name, which looks like what
you're trying to do here. It might better to throw an error than
return nonsense (though possibly not worth the trouble).