Explicitly cast zero to std::size_t.
Explicitly cast zero to std::size_t.

Signed/unsigned mismatch causes compilation warnings
from Boost.Test macros implementation.

nanodbc/nanodbc,nanodbc/nanodbc,ChrisBFX/nanodbc,norsync/nanodbc,norsync/nanodbc,mcg1969/nanodbc,mcg1969/nanodbc,ChrisBFX/nanodbc