Fix task/translation.py reducemetric bleu issue #3338

[juheeuu]

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• [x] Did you write any new necessary tests?

What does this PR do?

Fix #3338. If the translation model works so bad, the max(totals) becomes 0. When this case, if the args best-checkpoint-metric bleu givens the training system produces an error. I try to fix this problem by logging zero bleu when max(totals) <= 0 case.

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[stale[bot]]

This pull request has been automatically marked as stale. If this pull request is still relevant, please leave any comment (for example, "bump"), and we'll keep it open. We are sorry that we haven't been able to prioritize reviewing it yet. Your contribution is very much appreciated.

[juheeuu]

bump