sasl: clear client object on deinitialization
sasl: clear client object on deinitialization

We usually clear the object to its NULL-state on deinitialization, so
follow this style for SASLClient.

Signed-off-by: David Herrmann <fb53b2ddb8d141e0cb39d7c67c2f81b6bc2eb0f7@gmail.com>

bus1/dbus-broker