bug#61704: 29.0.60; Crash in get_narrowed_begv

[Gregory Heytings]

> > I maintain that the bug is (was) most probably not in get_narrowed_*. I 
> > just built Emacs with the GTK, Lucid and no toolkits, I disabled 
> > everything (tool-bar, menu-bar, scroll-bar, fringe-mode 0), and even 
> > with that, after resizing the Emacs frame until it is literally a 
> > single pixel on screen, I'm not able to get (under emacs -Q) a window 
> > width or a height equal to 0 there.  The smallest values I get are 
> > width = 2 and height = 1.
>
> What you listed above is not likely to affect the height of a window - 
> it's the header, mode and tab lines that count more.

Yes, I disabled all this to make sure the frame (and therefore the windows 
on the frame) would become as small as possible.  I tested this with emacs 
-Q, with several windows on the frame displaying a buffer in which 
(long-line-optimizations-p) is non-nil, without any header line or tab 
line.

Perhaps I should have tried to disable the mode-line.  Let's see...

M-: (setq mode-line-format nil) RET

No, still no way to get a zero height or width.  Increasing or decreasing 
the font size in the buffer also has no effect, I can't get a zero height 
or width.

> Don't worry.  What Po Lu saw is something I've seen in different forms 
> much earlier.  Small frames can be a problem for redisplay.

Indeed.