protect when some batch is empty
protect when some batch is empty

OpenNMT/OpenNMT,jsenellart-systran/OpenNMT,cservan/OpenNMT_scores_0.2.0,jsenellart-systran/OpenNMT,jungikim/OpenNMT,OpenNMT/OpenNMT,jungikim/OpenNMT,jsenellart-systran/OpenNMT,monsieurzhang/OpenNMT,da03/OpenNMT,monsieurzhang/OpenNMT,monsieurzhang/OpenNMT,da03/OpenNMT,da03/OpenNMT,jsenellart/OpenNMT,jsenellart/OpenNMT,OpenNMT/OpenNMT,jungikim/OpenNMT,jsenellart/OpenNMT,srush/OpenNMT