bug#57353: [PATCH] Fix parse-colon-path with UNC directory names

[Eli Zaretskii]

> From: Richard Copley <rcopley@gmail.com>
> Date: Tue, 23 Aug 2022 12:34:02 +0100
> 
> A comment in `parse-colon-path' says:
> 
> ;; Previous implementation used `substitute-in-file-name'
> ;; which collapse multiple "/" in front.  Do the same for
> ;; backward compatibility.
> 
> However, `substitute-in-file-name' does not do that:
> 
> (substitute-in-file-name "//foo/a/b") // -> "//foo/a/b"

That is true, but:

  (substitute-in-file-name "///foo/a/b") => "//foo/a/b"

So it does collapse multiple "/", at least sometimes.  Moreover, the
above is on MS-Windows, but on GNU/Linux:

  (substitute-in-file-name "///foo/a/b") => "/foo/a/b"

So (a) this is system-dependent, and (b) substitute-in-file-name does
collapse multiple slashes, but preserves UNCs on MS-Windows.

Therefore, your patch needs some (minor) amendments.