Adds casts for 64-bit

Adds missing casts for 64-bit.
Removed zero initialization of hProvider. hProvider is an "out" parameter of CryptAcquireContextW.
Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/1142)