openvpn -- denial of service: client certificate validation can disconnect unrelated clients

James Yonan reports:

DoS attack against server when run with “verb 0” and
without “tls-auth”. If a client connection to the server
fails certificate verification, the OpenSSL error queue is
not properly flushed, which can result in another unrelated
client instance on the server seeing the error and
responding to it, resulting in disconnection of the
unrelated client.