bug#23871: 25.1.50; Undo unexpectedly leads to blank buffer

[Eli Zaretskii]

> From: Markus Triska <triska@metalevel.at>
> Cc: Eli Zaretskii <eliz@gnu.org>,  23871@debbugs.gnu.org
> Date: Fri, 01 Jul 2016 08:31:10 +0200
> 
> phillip.lord@russet.org.uk (Phillip Lord) writes:
> 
> > I believe the following patch fixes #21722.
> 
> I tried it, and can still reproduce both #21722 and #23871 also with the
> patch applied to the current emacs-25 branch.

Which doesn't surprise me, since point is at the insertion position
just before the insertion, which is when record_insert is called,
AFAIU.

I think the question here is why does undo record the position of
point at the end of the sexp, and not where point was when C-M-x was
invoked.  This has something to do with code that runs off C-M-x, I
presume.