bug#2571: 23.0.91; Crashes on zooming pdf document

[Chong Yidong]

> 0) emacs -Q

> 1) Open a pdf document, for example this one:

>    http://www.adobe.com/devnet/acrobat/pdfs/adobe_supplement_iso32000.pdf

> 2) Hit S-`+' several times. Emacs crashes once the width of the
>    document page becomes wider than the window.

I can't reproduce this.  Could you run Emacs within GDB and get a
backtrace?  (You should make sure that Emacs is compiled with debugging
symbols, and ideally with no optimizations; `CFLAGS="-g" ./configure'
will do that.)