Free plugin identifier.

src/security_default.c

@@ -180,12 +180,16 @@ int mosquitto_security_cleanup_default(struct mosquitto_db *db, bool reload)
 			if(db->config->listeners[i].security_options.pid){
 				mosquitto_callback_unregister(db->config->listeners[i].security_options.pid,
 						MOSQ_EVT_BASIC_AUTH, mosquitto_unpwd_check_default, NULL);
+
+				mosquitto__free(db->config->listeners[i].security_options.pid);
 			}
 		}
 	}else{
 		if(db->config->security_options.pid){
 			mosquitto_callback_unregister(db->config->security_options.pid,
 					MOSQ_EVT_BASIC_AUTH, mosquitto_unpwd_check_default, NULL);
+
+			mosquitto__free(db->config->security_options.pid);
 		}
 	}
 	return MOSQ_ERR_SUCCESS;