Add an error message when the beam size is smaller than the n-best list
Add an error message when the beam size is smaller than the n-best list

Fixes #219.

jungikim/OpenNMT,jungikim/OpenNMT,jsenellart/OpenNMT,jsenellart/OpenNMT,jsenellart-systran/OpenNMT,jungikim/OpenNMT,jsenellart-systran/OpenNMT,monsieurzhang/OpenNMT,OpenNMT/OpenNMT,OpenNMT/OpenNMT,jsenellart/OpenNMT,da03/OpenNMT,da03/OpenNMT,jsenellart-systran/OpenNMT,monsieurzhang/OpenNMT,da03/OpenNMT,OpenNMT/OpenNMT,monsieurzhang/OpenNMT