Description:
------------
For some reason the root <book> chunk loses its name when there is an 
empty <index /> element in the body

Reproduce code:
---------------
Taken from the Zend Framework manual:

<book xmlns="http://docbook.org/ns/docbook" version="5.0" xml:id="manual" xml:lang="en">
    <info><title>Programmer's Reference Guide</title><subtitle>Zend Framework</subtitle>
               
               
        <copyright>
            <holder>
                Zend Technologies Inc.
                (<uri xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://www.zend.com">http://www.zend.com</uri>)
            </holder>
        </copyright>
    </info>

    <index xml:id="the.index" />
</book>


Expected result:
----------------
a manual.html page and an empty index <div>

Actual result:
--------------
a file called ".html"