Fix BN_mod_word bug
Fix BN_mod_word bug

On systems where we do not have BN_ULLONG (e.g. typically 64 bit systems)
then BN_mod_word() can return incorrect results if the supplied modulus is
too big.

RT#4501

Reviewed-by: Andy Polyakov <015edf36635e030d5e009e08808a59984e629740@openssl.org>

openssl/openssl,openssl/openssl,openssl/openssl,openssl/openssl,openssl/openssl,openssl/openssl