[Bugfix] Fix logits processor when prompt_logprobs is not None

[huyiwen]

This is a resubmission of #3023.

This handles prompt_logprobs by skipping rows in logits added for the prompt tokens (prompt logprobs are not processed)

Comparing to the previous one, this pr resolves the comment of @tjohnson31415.

Related issue: #2141
Related PR: #2800
FIX #2800

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[njhill]

@huyiwen any chance you could add a unit test for this too? 🙏

[njhill]

Thanks again @huyiwen!

[njhill]

Thanks for the contribution @huyiwen