[xml] Access internal xmlParserInputBuffer data

[Nikolay Sivov <bunglehead gmail com>]

Hi.

First on question background. I want to use xmlTextReader API to access 
streamed xml data.
Decided to allocate input buffer with xmlAllocParserInputBuffer() and 
use read callback to provide xml data
(no choice here for me actually).

Is it safe to manually set 'readcallback' and 'context' fields of 
returned xmlParserInputBuffer?
Looking at libxml2 code I don't see any problems with that, but it's 
better to ask.