fix: 修复异常断开的指标统计

services/mqttaccess/mqtt_provider.go

@@ -45,7 +45,9 @@ func (mp *MQTTProvider) OnDeviceOnline(args rpcs.ArgsGetOnline, VendorId string)
 	return err
 }
 func (mp *MQTTProvider) OnDeviceOffline(deviceid string, vendorId string) error {
-	deviceOnlineCount.Dec()
+	if deviceid != "" {
+		deviceOnlineCount.Dec()
+	}
 	args := rpcs.ArgsGetOffline{
 		Id:       deviceid,
 		VendorId: vendorId,