Avoid implicit cast from size_t to int in a test
Avoid implicit cast from size_t to int in a test

This fixes another -Wconversion warning given by g++ 4.8 but,
surprisingly, not later versions for some reason.

vslavik/xmlwrapp,vslavik/xmlwrapp,vadz/xmlwrapp,vadz/xmlwrapp,vadz/xmlwrapp,vslavik/xmlwrapp