[GSS](7.1.0) SSLHeaderHandler should not require base64 SSL_SESSION_ID

SSLHeaderHandler strictly expects the SSL_SESSION_ID header to be present currently with a base64 encoded value. If the SSL_SESSION_ID header is not present, SSLHeaderHandler does nothing and no other ssl info headers are handled. If the SSL_SESSION_ID header does not contain a base64 value, then SSLHeaderHandler/BasicSSLSessionInfo fails the request with a RuntimeException. That can occur with httpd in front since httpd/mod_ssl/openssl can provide a ssl_session_id header value of (null).

This should be improved so that:

1. SSLHeaderHandler/BasicSSLSessionInfo does not fail requests with non-base64 SSL_SESSION_ID header values
2. SSLHeaderHandler still handles other ssl info headers regardless of SSL_SESSION_ID's presence or value