mod_ssl: We need to get the SSL_CTX for further processing

mod_ssl: We need to get the SSL_CTX for further processing
down below.

This fixes a crash during SSL renegotiation with OptRenegotiate set,
when client certificates are available from the original handshake
but were originally not verified and should get verified now.
This is a regression in 2.4.36 (unreleased).

Backport of r1828793 from trunk.

Submitted by: rjung
Reviewed by: rjung, rpluem, jorton

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1844223 13f79535-47bb-0310-9956-ffa450edef68