bug#30285: dired-do-chmod vs. top line of dired

[Tino Calancha]

On Thu, 1 Feb 2018, Juri Linkov wrote:

> Oh, and I discovered that the current state is much worse than I thought:
>
> 1. load dired-x
> 2. type ‘M-<’ to go to the first line
> 3. type ‘!’ (dired-do-shell-command)
>
>  “Wrong type argument: stringp, nil”
Is it too much ask you to read my commit messages in case you dont
have time/motivation to test my patches?  Then, you dont need to
rediscover things already reported by others.  Thanks.

Some people say here they dont have time to tes my patches (even
to read my commit messages), but at the same time they write
the Bible in their emails (by the way, not refering to you now).

I do sleep 3 hours every day, more busy that all of you together
and I still tested your patch and read (entirely) others emails.

PD: By the way, I have tested your patch, and it looks good to me.  It 
fixes the issue in a quite simple way.