Add exception for bsz=1 with prefix generation (#796)
Add exception for bsz=1 with prefix generation (#796)

Summary:
This is a temporary workaround to support sampling after https://github.com/pytorch/fairseq/issues/713. We'll need to revisit this to support sampling and beam more generally.
Pull Request resolved: https://github.com/pytorch/fairseq/pull/796

Differential Revision: D15760808

Pulled By: myleott

fbshipit-source-id: ecaf4f161b0c30de037f32007e4610a559a49230

pytorch/fairseq,pytorch/fairseq,pytorch/fairseq