Fixed chunk size calculation

[sjha2048]

This pull request rectifies the chunk file calculation

Fixes: #17

[simonmichal]

Hello,
Thank you for submitting a PR, however this repo is no longer active, xrootd-python is now part of core xrootd repo and from what I see the problem has been already fixed:
https://github.com/xrootd/xrootd/blob/master/bindings/python/src/PyXRootDFile.cc#L252

Cheers,
Michal

[sjha2048]

Thanks for pointing it out @simonmichal