Fix Constrained beam search duplication and weird output issue
Author: boy2000-007man
Pull request: yes

# What does this PR do?

- prevent duplicates between *(topk) generic beam search best model next tokens* and *(advance) constraints forcing the next token*
- ensure unfulfilled hypothesis will advance with correct beam score instead of wrong token score

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Fixes # (issue)

#17812 

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## Who can review?

@patrickvonplaten

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Comments:
_The documentation is not available anymore as the PR was closed or merged._

@cwkeam - do you have an idea here?

Good catch @boy2000-007man !! @patrickvonplaten I just read through the issue and saw the code changes and they're all right-on. Thanks for finding these problems!

Thank you for this fix! I found this pull request while I was searching to figure out why constrained beam search was churning out such repetitive results on 4.20.1. Installing the current repo of transformers fixed this immediately!