Some bug in using eval_all_checkpoints
when using --eval_all_checkpoints
checkpoints will find a pytorch_model.bin just under output_dir
when calling evaluate(args, model, tokenizer, prefix=global_step) will get a FileNotFoundError
# [Codecov](https://codecov.io/gh/huggingface/transformers/pull/2105?src=pr&el=h1) Report
> Merging [#2105](https://codecov.io/gh/huggingface/transformers/pull/2105?src=pr&el=desc) into [master](https://codecov.io/gh/huggingface/transformers/commit/0cb163865a4c761c226b151283309eedb2b1ca4d?src=pr&el=desc) will **not change** coverage.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/huggingface/transformers/pull/2105/graphs/tree.svg?width=650&token=9qOlN6Hb1c&height=150&src=pr)](https://codecov.io/gh/huggingface/transformers/pull/2105?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master    #2105   +/-   ##
=======================================
  Coverage   82.67%   82.67%           
=======================================
  Files         111      111           
  Lines       16162    16162           
=======================================
  Hits        13362    13362           
  Misses       2800     2800
```



------

[Continue to review full report at Codecov](https://codecov.io/gh/huggingface/transformers/pull/2105?src=pr&el=continue).
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> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/huggingface/transformers/pull/2105?src=pr&el=footer). Last update [0cb1638...4757840](https://codecov.io/gh/huggingface/transformers/pull/2105?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
<|||||>This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.
