mod_ssl: SSL_smart_shutdown(): follow up to r1601184.
Use SSL_get_wbio() to comply with OPENSSL_NO_SSL_INTERN.
Stop SSL shutdown loop when flush fails.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1601274 13f79535-47bb-0310-9956-ffa450edef68