Add back try/except in data_utils
Add back try/except in data_utils

Summary: Accidentally removed try/except block in D27194569 (https://github.com/pytorch/fairseq/commit/a28511d43d2310226086c5fee82042fcdcf4cff0) and caused OSS unit test failure.

Reviewed By: myleott

Differential Revision: D27374072

fbshipit-source-id: 154c92eae106aa3bf6b406d52a8647db140dc6b3

pytorch/fairseq,pytorch/fairseq,pytorch/fairseq