[racket] Scribble index missing when generating pdf file

It looks like index output for the Latex/PDF back end has been broken
for a while. I'll fix it.

At Sat, 24 Jan 2015 17:38:54 +0100, Jens Axel Søgaard wrote:
> Hi All.
> 
> The following document when rendered to HTML gives a nice index.
> However when rendered to PDF the index page just has the "Index"
> header, but the page is otherwise blank.
> 
> I use the buttons from within DrRacket to render to two formats.
> 
> What am I missing?
> 
> #lang scribble/base
> @title{Testing index}
> @section{First section}
> @subsection{A subsection of the first section}
> Some @as-index{text}.
> @section{Second section}
> @(index-section)
> 
> /Jens Axel
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