Fixing batching pipelines on single items for ChunkPipeline
Author: Narsil
Pull request: yes

# What does this PR do?

Fixing #20783

The issue was that the iterator would not be called because of the input type.
Regardless of the input type, `ChunkPipeline` will always potentially be iterating over
its inputs in order to use batching.

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Fixes # (issue)


## Before submitting
- [ ] This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
- [ ] Did you read the [contributor guideline](https://github.com/huggingface/transformers/blob/main/CONTRIBUTING.md#start-contributing-pull-requests),
      Pull Request section?
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      [here are tips on formatting docstrings](https://github.com/huggingface/transformers/tree/main/docs#writing-source-documentation).
- [ ] Did you write any new necessary tests?


## Who can review?

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Comments:
_The documentation is not available anymore as the PR was closed or merged._