Return empty handler if rgb doesn't exist when trying to add alpha value (#5415)

* So error and return empty callback, as the ply header is illdefined (for pcl at least).

* Return bool with true as succes for amendProperty.

Author: larshg

io/include/pcl/io/ply_io.h

@@ -448,10 +448,13 @@ namespace pcl
 
       /** Amend property from cloud fields identified by \a old_name renaming
         * it \a new_name.
+        *  * Returns:
+        *  * false on error
+        *  * true success
         * param[in] old_name property old name
         * param[in] new_name property new name
         */
-      void
+      bool
       amendProperty (const std::string& old_name, const std::string& new_name, std::uint8_t datatype = 0);
 
       /** Callback function for the begin of vertex line */

io/src/ply_io.cpp

@@ -115,23 +115,22 @@ pcl::PLYReader::appendScalarProperty (const std::string& name, const std::size_t
   cloud_->point_step += static_cast<std::uint32_t> (pcl::getFieldSize (pcl::traits::asEnum<Scalar>::value) * size);
 }
 
-void
+bool
 pcl::PLYReader::amendProperty (const std::string& old_name, const std::string& new_name, std::uint8_t new_datatype)
 {
-  auto finder = cloud_->fields.rbegin ();
-  for (; finder != cloud_->fields.rend (); ++finder)
-    if (finder->name == old_name)
-      break;
-  if (finder == cloud_->fields.rend ())
-  {
-      PCL_ERROR("[pcl::PLYReader::amendProperty] old_name '%s' was not found in cloud_->fields!\n",
-          old_name.c_str());
-      assert (false);
-      return;
+  const auto fieldIndex = pcl::getFieldIndex(*cloud_, old_name);
+  if (fieldIndex == -1) {
+    return false;
   }
-  finder->name = new_name;
-  if (new_datatype > 0 && new_datatype != finder->datatype)
-    finder->datatype = new_datatype;
+
+  auto& field = cloud_->fields[fieldIndex];
+
+  field.name = new_name;
+  
+  if (new_datatype > 0 && new_datatype != field.datatype)
+    field.datatype = new_datatype;
+
+  return true;
 }
 
 namespace pcl
@@ -213,7 +212,15 @@ namespace pcl
       }
       if (property_name == "alpha")
       {
-        amendProperty ("rgb", "rgba", pcl::PCLPointField::UINT32);
+        if (!amendProperty("rgb", "rgba", pcl::PCLPointField::UINT32))
+        {
+          PCL_ERROR("[pcl::PLYReader::scalarPropertyDefinitionCallback] 'rgb' was not "
+                    "found in cloud_->fields!,"
+                    " can't amend property '%s' to get new type 'rgba' \n",
+                    property_name.c_str());
+          return {};
+        }
+        
         return [this] (pcl::io::ply::uint8 alpha) { vertexAlphaCallback (alpha); };
       }
       if (property_name == "intensity")