adds debug message in case of read_value failure

cpp/hdf5_tools.cpp

@@ -219,7 +219,11 @@ number hdf5_tools::read_value(
     if (H5Lexists(group, dset_name.c_str(), H5P_DEFAULT))
     {
         dset = H5Dopen(group, dset_name.c_str(), H5P_DEFAULT);
-        H5Dread(dset, mem_dtype, H5S_ALL, H5S_ALL, H5P_DEFAULT, &result);
+        herr_t status = H5Dread(dset, mem_dtype, H5S_ALL, H5S_ALL, H5P_DEFAULT, &result);
+        if (status < 0)
+        {
+            DEBUG_MSG("had an error trying to read %s.\n H5Dread returned status %ld\n", dset_name.c_str(), status);
+        }
         H5Dclose(dset);
     }
     else