Updated so libgdf groupby call will not return an error if the input is empty and instead returns GDF_SUCCESS.
Updated so libgdf groupby call will not return an error if the input is empty and instead returns GDF_SUCCESS.

gpuopenanalytics/libgdf,gpuopenanalytics/libgdf,gpuopenanalytics/libgdf,gpuopenanalytics/libgdf