bug#24471: 25.1.50; Error on empty PATH component

[Eli Zaretskii]

> From: Noam Postavsky <npostavs@users.sourceforge.net>
> Date: Thu, 22 Sep 2016 18:28:46 -0400
> Cc: Achim Gratz <Stromeko@nexgo.de>, 24471@debbugs.gnu.org
> 
> Ah, the custom :standard value is different from the initial value,
> which uses decode_env_path. Is it possible to use the same code for
> both? It seems that decode_env_path handles some extra things: file
> name encoding, checking for file name handlers.

File name encoding should not be the problem, because the Lisp getenv
takes care of that already (see make_string).  As for file-name
handlers, do we expect PATH to include such file names?
(decode_env_path is more general, and used not just for PATH.)