bug#18597: 25.0.50; Assertion violation in reseat_1

[martin rudalics]

> This says that the window's start position is 1 and also that position
> 2658017 is inside the window.  Is that reasonable?

Hardly.

> What does this show:
>
>    (gdb) frame 9
>    (gdb) p w->start

(gdb) frame 9
#9  0x010984f0 in window_scroll_pixel_based (window=..., n=-5, whole=false, 
noerror=0) at window.c:4920
4920      if (!pos_visible_p (w, PT, &x, &y, &rtop, &rbot, &rowh, &vpos))
(gdb) p w->start
$8 = {
  i = 24813235
}

martin