controller: Ignore log messages unrelated to IKE_SA affected by a command

Until we know which IKE_SA is affected by an initiate() or terminate_*()
command, unrelated log messages that don't have any IKE context (i.e.
the passed `ike_sa` is NULL) would previously get logged.

src/libcharon/control/controller.c

@@ -228,7 +228,7 @@ METHOD(logger_t, listener_log, void,
 	target = this->listener->ike_sa;
 	this->listener->lock->unlock(this->listener->lock);
 
-	if (target == ike_sa)
+	if (target && target == ike_sa)
 	{
 		if (!this->callback(this->param, group, level, ike_sa, message))
 		{