SSL: clear error queue after OPENSSL_init_ssl().

SSL: clear error queue after OPENSSL_init_ssl().

The function may leave error in the error queue while returning success,
e.g., when taking a DSO reference to itself as of OpenSSL 1.1.0d:
https://git.openssl.org/?p=openssl.git;a=commit;h=4af9f7f

Notably, this fixes alert seen with statically linked OpenSSL on some platforms.

While here, check OPENSSL_init_ssl() return value.