Merge r1588853 from trunk:

ssl_stapling_init_cert: do not return success when no responder URI is found
stapling_renew_response: abort early (before apr_uri_parse) if ocspuri is empty

Submitted by: kbrand
Reviewed/backported by: jim


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1593002 13f79535-47bb-0310-9956-ffa450edef68