mod_ssl: Follow up to r1913815: szCryptoDevice to NULL when !MODSSL_HAVE_ENGINE_API

mod_ssl: Follow up to r1913815: szCryptoDevice to NULL when !MODSSL_HAVE_ENGINE_API

Latest OpenSSL versions removed the ENGINE API completely, still provide NULL
SSLModConfigRec::szCryptoDevice since it's used outside MODSSL_HAVE_ENGINE_API.

SSLModConfigRec is a private struct, so no MMN change.

* modules/ssl/ssl_private(SSLModConfigRec):
  Provide szCryptoDevice (NULL) even if !MODSSL_HAVE_ENGINE_API.

Merges r1915889 from https://svn.apache.org/repos/asf/httpd/httpd/trunk.

Submitted by: ylavic
Reviewed by: ylavic, jorton, jfclere

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1915949 13f79535-47bb-0310-9956-ffa450edef68