Self-chat batch size assertion error (#3081)
Self-chat batch size assertion error (#3081)

* Add assertion error

* nit

Co-authored-by: Diana Rico <968a68c13f7bb6626c1656f04e48230ab0522e55@learnfair0721.h2.fair>
facebookresearch/ParlAI,facebookresearch/ParlAI,facebookresearch/ParlAI,facebookresearch/ParlAI,facebookresearch/ParlAI