Fix attn_mask bug in TransformerEncoderLayer (only affects speech_recognition example) (#1018)
Fix attn_mask bug in TransformerEncoderLayer (only affects speech_recognition example) (#1018)

Summary:
Fixes #1339.
Pull Request resolved: https://github.com/fairinternal/fairseq-py/pull/1018

Differential Revision: D19796152

Pulled By: myleott

fbshipit-source-id: e2304a549c52804d2b5c4c9b31f8d852827ae943

pytorch/fairseq,pytorch/fairseq,pytorch/fairseq