Merge r1756542 from trunk:

mod_ssl: Fix quick renegotiation (OptRenegotiaton) with no intermediate
in the client certificate chain.  PR 55786.

This is done by handling an empty cert chain as no/NULL chain.


Submitted by: ylavic
Reviewed/backported by: jim


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1770838 13f79535-47bb-0310-9956-ffa450edef68