bug#64298: 29.0.92; Fixes for several todo-mode bugs

[Eli Zaretskii]

> From: Stephen Berman <stephen.berman@gmx.net>
> Date: Mon, 26 Jun 2023 11:39:35 +0200
> 
> This report describes and provides patches for four different bugs in
> todo-mode.el.  Three of the bugs can result in todo-mode file format
> corruption, and the fourth is a documentation bug, so I think the fixes
> should all be installed in the release branch, and I'm asking for
> permission to do that.  As with my previous todo-mode bugfix, which also
> went into the release branch (bug#63811), the patches touch only
> todo-mode.el and with them all todo-mode unit tests pass.

The 3rd and the 4th patches are okay for the release branch.  The
first one looks OK, but how sure you are that you have identified all
the places which need buffer-read-only bound to nil?  Did you exercise
all the possible code paths in the places affected by this change?

The 2nd patch is the scariest.  How grave is it, and if it's grave,
how come it was not reported until now?  In general, I'd prefer to
have the 2nd patch on master, not on the release branch, at least for
now.  (We could consider backporting it after Emacs 29.1 is released.)

Thanks.