bug#11964: describe-char causes a fatal error (abort trap: 6) in non-windowed mode

[Eli Zaretskii]

> From: Chong Yidong <cyd@gnu.org>
> Cc: Jan Djärv <jan.h.d@swipnet.se>,
>   ninestraycats@gmail.com,  11964@debbugs.gnu.org
> Date: Mon, 26 Nov 2012 11:55:32 +0800
> 
> Thanks for the patch.  But I'm not sure this is 100% fixed yet: calling
> internal-char-font on a tty should not crash Emacs, since Lisp calls
> should never cause a crash.  So I think internal-char-font should return
> nil if the seleced frame is non-graphical.

Done in revision 110962 on the emacs-24 branch.