[tex4ht] Indices don't show up in the Table of Contents

[Michal Hoftich]

Hi Jürgen,

> When creating documents with indices with imakeidx and then generating a table of contents with \tableofcontents , the indices show in the Table of Contents in the PDF document - but not in the epub document.
>

This looks like a bug in TeX4ebook. I hope that I've fixed that in the
sources. But your fix works as well, which is nice.

Best regards,
Michal