bug#24471: 25.1.50; Error on empty PATH component

[Eli Zaretskii]

> From: Achim Gratz <Stromeko@nexgo.de>
> Date: Thu, 22 Sep 2016 22:10:43 +0200
> 
> Eli Zaretskii writes:
> > Thanks.  Does the patch below fix the problem?
> 
> Thanks.  I have no doubt it will, but I can't test it for a few days.

Thanks, I'll wait.

Another issue is whether we want to filter out nil or leave it alone
(i.e. change the function used by mapcar so it skips nil elements)?
Any thoughts on this one?