bug#10696: 24.0.93; crash by null string display property

[Eli Zaretskii]

> From: Kenichi Handa <handa@m17n.org>
> Date: Thu, 02 Feb 2012 22:17:58 +0900
> 
> Emacs crashes by this scenario.
> 
> Start Emacs under gdb as this
> 
> % cd .../emacs/src
> % gdb emacs
> (gdb) run -Q
> 
> Then type this in *scratch* buffer.
> 
> (put-text-property 1 3 'display "")C-j
> ESC < C-f C-b
> 
> Then Emacs abort as this.
> 
> Breakpoint 1, abort () at emacs.c:394
> (gdb) bt full
> #0  abort () at emacs.c:394
> No locals.
> #1  0x0817b0f6 in buf_charpos_to_bytepos (b=0x8486dd0, charpos=0)
>     at marker.c:130

Fixed in revision 107088 on the trunk.