Modify ssl_handshake_hash to call SSLfatal

Modify ssl_handshake_hash to call SSLfatal

When EVP_MD_CTX_new fails call SSLfatal before the goto err.
This resolves a state machine issue on the out of memory condition:
ssl/statem/statem.c:643: OpenSSL internal error: Assertion failed:
(s)->statem.in_init && (s)->statem.state == MSG_FLOW_ERROR

Fixes #15491.
CLA: trivial

Reviewed-by: Ben Kaduk <kaduk@mit.edu>
Reviewed-by: Paul Dale <pauli@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/15511)