Add checks to the return value of EVP_Cipher to prevent silent encryption failure.

PR#1767

Reviewed-by: Richard Levitte <levitte@openssl.org>
Check EVP_Cipher return values for SSL2

Reviewed-by: Richard Levitte <levitte@openssl.org>
Fixed warning in ssl2_enc

Reviewed-by: Richard Levitte <levitte@openssl.org>