bug#47244: 28.0.50; SIGSEGV in long-runnning Emacs

[martin rudalics]

> Using watchpoints on Vwindow_list that are turned off when in
> window_list() and ignored when it is set to nil, I was at least able to
> determine that whatever is modifying the list is doing so destructively,
> not by setting a new value.

Since I don't believe in miracles I expected that.  But I've been
searching our code base repeatedly and nowhere found a clue that that
list - the return value of window_list - would be modified in such a
deterministic and orderly way.  Maybe I'm blind already.

martin