[xml] how to get xmlTextReaderLocatorPtr from a xmlTextReaderPtr

[David Hagood <wowbagger sktc net>]

Suppose that I am processing a file via an xmlTextReaderPtr, and I want to
call the same error handler routine as the xmlTextReaderPtr will. That
routine's signature is

void    xmlTextReaderErrorFunc          (void * arg,
                                         const char * msg,
                                         xmlParserSeverities severity,
                                         xmlTextReaderLocatorPtr locator)

So if I want to call it, I have to create or get an xmlTextReaderLocatorPtr.

While there are several routines for querying an xmlTextReaderPtr and
getting line numbers and the like, there are no routines I can find that
give me the xmlTextReaderLocatorPtr.

Am I missing something?