bug#22356: 25.0.50; emacs-25 very crashy with ivy-mode

[Eli Zaretskii <eliz@gnu.org>]

> From: Óscar Fuentes <ofv@wanadoo.es>
> Date: Wed, 13 Jan 2016 02:36:26 +0100
> Cc: 22356@debbugs.gnu.org
> 
> Dmitry Gutov <dgutov@yandex.ru> writes:
> 
> >> But it seems to work fine on
> >>
> >> GNU Emacs 25.0.50.1 (i686-w64-mingw32) of 2015-05-13 on CAB8
> >
> > I haven't tried this version exactly, but I can reproduce it in Emacs
> > 24.5 release, too.
> 
> On that Windows install I can type C-q C-j on the minibuffer many times
> without problem (on the GNU/Linux Emacs freezes after the second C-q
> C-j). However, Emacs crashes while exiting when the window's decoration
> Close button is clicked.
> 
> The many faces of memory corruption.

We weren't assigning space for glyphs of the margins in the
mini-window.  Why? because of a single typo (or thinko?) more than 2
years ago!  That typo made us think the mini-window has a very large
total width in column units:

  emacs -Q
  M-: (window-total-width (minibuffer-window)) RET
    => 672

That preposterous value then defeated the logic in the display engine
which decides how many glyphs are needed for displaying stuff in the
margin, when margins are turned on in a window: that logic decided the
correct number was zero.  And from there it's a quick path to writing
beyond the allocated memory.

Should be fixed now on the emacs-25 branch.  But since the phenomena I
saw on my system are different from what was reported here, please
make sure your problems are also solved, not just mine.

Thanks.