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

[martin rudalics]

> Maybe instead of trying to find the exact culprit, we should simply
> protect this code:
>
>        /* Make sure the current window's buffer is selected.  */
>        set_buffer_internal (XBUFFER (XWINDOW (selected_window)->contents));
>
> from selecting a dead buffer?  For example, by using
> other_buffer_safely if the selected-window's buffer is dead.

The problem is that we already detect this situation too late in order
to tell who the real culprit is.  For example, a dead buffer stored in
the selected_window's contents field could have been a dead
current_buffer before.  So for some time we could have been already
running with a dead buffer in that filed.  Long enough maybe to cause
havoc elsewhere.  And what happened in between might not have used
set_buffer_internal but accessed that buffer more directly.

martin