CryptBinaryToString() returns, when passed aNULL buffer, not size of the
encoded string, but size of the buffer requires, i.e. including the
trailing null.
The code incorrectly used this value to as std::string's size, resulting
in embedded trailing null in the output.
Fix by sizing the string properly. Note that this is safe in C++17,
which we rely on by using non-const data(): the buffer returned by
data() is guaranteed to be terminated with a trailing '\0' and this
value is writeable, as long as the value written is '\0' - which is what
CryptBinaryToString() will do.
Fixes#289.
Václav Slavík
5e2ad7cb1e