Merge r1630947, r1645670 from trunk

   * mod_ssl: Check if we are having an SSL connection before looking up SSL
              related variables during expression evaluation to avoid a crash.
              If not return NULL as ssl_var_lookup_ssl does by default.  PR 57070

Submitted by: rpluem
Reviewed by: jailletc36, ylavic, covener
Backported by: jailletc36

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1650659 13f79535-47bb-0310-9956-ffa450edef68