bug#11850: bug#11813: bug#11850: crash (null font) running emacs built from git

[Eli Zaretskii]

> Date: Wed, 04 Jul 2012 19:32:01 +0300
> From: Eli Zaretskii <eliz@gnu.org>
> Cc: 11850@debbugs.gnu.org, 11813@debbugs.gnu.org
> 
> Next, please apply the patch below, and tell me whether one of the
> assertions I've added catches our villain.  If it does, please show
> the backtrace.

I forgot to tell: for these asserts to be in effect, you need to rerun
the configure script passing it the --enable-checking switch, then
rebuild (without optimizations).