Fix data field for scalar structures with no fields in HDF format
Fix data field for scalar structures with no fields in HDF format

* src/mat73.c (Mat_H5ReadGroupInfo): Return early if there are no fields
      which happens with early HDF5 schema which does not use a dataset
      for structures with no fields

tbeu/matio,NJannasch/matio,martinichka/matio-coder,martinichka/matio-coder,MaartenBent/matio,tbeu/matio,NJannasch/matio,telehan/libmatio,CBL-ORION/matio-sf-mirror,MaartenBent/matio,martinichka/matio-coder,telehan/libmatio,CBL-ORION/matio-sf-mirror,MaartenBent/matio,CBL-ORION/matio,CBL-ORION/matio,tbeu/matio,tbeu/matio,MaartenBent/matio