when client_attrs_init expression renders to empty string,
do not initialize the attribute.
also fixed an ACL error: a template render failure for a topic
would stop the ACL checks for the following topics if more
than one topic is configured.
Move authz result logging to common place.
Prior to this change, the final result is not logged when
fallback to the default authorization.no_match config value.
Aso, if the result is provided by a hook callback,
it's also not logged.
After this change, only the final result is logged.
The authz chain resutls can be traced (or logged at debug level).
zmstone