Fix access zero memory if SSL_DEBUG is enabled

If compile OpenSSL with SSL_DEBUG macro, some test cases will cause the
process crashed in the debug code.

Reviewed-by: Tim Hudson <tjh@openssl.org>
Reviewed-by: Paul Dale <paul.dale@oracle.com>
(Merged from https://github.com/openssl/openssl/pull/7707)

(cherry picked from commit 5a4481f0)