Fix infinite recursion of md5 calculation on Windows
Fix infinite recursion of md5 calculation on Windows

Was caused by some safety things of making sure we've for NULL
terminator for the buffer when doing mbs<->wcs conversion, but
it turns out this simply confuses str::string and it can no
longer have proper .size(). Let's assume behavior of string
allocation is same all over the std, and we can avoid having
that extra null-terminator allocated.

tangent-opensource/coreBlackbird,tangent-opensource/coreBlackbird,tangent-opensource/coreBlackbird