bug#11802: 24.1; Error when viewing message with face header in Gnus

[Chong Yidong]

Frank Schmitt <ich@frank-schmitt.net> writes:

> I have GNU emacs configured without X running inside GNU screen. When I
> open a message containing a face header (e.g. those by Larsi), I get:
>
> Debugger entered--Lisp error: (error "Not an image: nil")
>   signal(error ("Not an image: nil"))
>   error("Not an image: %s" nil)
>   insert-image(nil " ")
>   gnus-put-image(nil nil face)

I committed a fix to trunk.  Thanks.