bug#30938: 27.0; `dired-do-create-files' etc.: do NOT always raise error if no files

[Drew Adams]

> > If you don't believe that a user or another library could
> > or would define such a command (or in any other way would
> > call an existing function that calls the workhorse function
> > `dired-get-marked-files', then too bad.
> 
> Such uses can always call dired-get-marked-files with the last
> argument nil or omitted.  Where's the problem?

I won't repeat myself this time.  If you don't want to see or
fix the problem, so be it.