bug#31492: 26.1; query-replace-regexp undo fails in regexps w/o printable chars

[Tino Calancha]

On Fri, 18 May 2018, Eli Zaretskii wrote:

> > From: Tino Calancha <tino.calancha@gmail.com>
> > Date: Fri, 18 May 2018 22:27:36 +0900
> >
> > emacs -Q
> >
> > < C-M-% \b RET foo RET TAB TAB TAB
> > U ; undo all replacements
> > ;; Nothing is undid :-(
>
> I'm probably missing something, because I cannot reproduce the problem
> I guess the explanation is in what does "<" mean and, more
'<' stands for `beginning-of-buffer'.  Then you have text to replace in 
the *scratch* buffer.  Otherwise you at the end of the buffer and my
regexp cannot match.