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

[Eli Zaretskii]

> From: phillip.lord@russet.org.uk (Phillip Lord)
> Cc: Eli Zaretskii <eliz@gnu.org>,  23871@debbugs.gnu.org
> Date: Sun, 03 Jul 2016 13:55:48 +0100
> 
> I've tried to reproduce #23871, but unfortunately, swiprolog crashes as
> shown below.

I very much hope that the problem could be reproduced without using
Prolog at all, by just invoking a program like 'cat' to insert some
text into the buffer.  I cannot see how Prolog can be possibly
relevant to this, as all it does is insert text into the buffer.

> The packaged version of swiprolog on my machine is 6.6.4, rather than >
> 7.2. I'm not keen on trying to update to 7.2.

Actually, the recipe asks for 7.3.