add an empty cloud condition. make it more natural.

src/wj_lidar/region_detect.cpp

@@ -263,6 +263,8 @@ Error_manager Region_detector::clustering(pcl::PointCloud<pcl::PointXYZ>::Ptr cl
     clustering.setInputCloud(cloud_in);
     std::vector<pcl::PointIndices> clusters;
     clustering.extract(clusters);
+    if(clusters.size() <= 0)
+        return Error_manager(Error_code::WJ_REGION_EMPTY_CLOUD);
 
     for (int i = 0; i < clusters.size(); ++i)
     {