Also clear the error queue before calling SSL_CTX_use_certificate[_chain]_file
(workaround for OpenSSL versions before 0.9.8h, see
https://rt.openssl.org/Ticket/Display.html?user=guest&pass=guest&id=1513).

PR 56410.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1588427 13f79535-47bb-0310-9956-ffa450edef68