bug#13066: 24.2.90; setting rmail-summary-window-size causes error

[martin rudalics]

> When I customize rmail-summary-window-size to some integer
> value (e.g. 10), M-x rmail-summary signals this error:
>
>    Wrong type argument: stringp, nil
>
> This is with emacs-24 branch.  This doesn't happen with
> Emacs 23, but I don't remember it happens with 24.1 and 24.2.
>
> The precise recipe:
> % emacs -Q
> M-x rmail RET
> M-x customize-variable RET rmail-summary-window-size
> ;; Then set it to 10, click [apply], type q, then type h

I can't reproduce that here.  Can you post a backtrace, please.

martin