fix: create child chunk

[devxing]

Summary

fix create child chunk bug
Resolves #18208

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Checklist

Important

Please review the checklist below before submitting your pull request.

• This change requires a documentation update, included: Dify Document
• I understand that this PR may be closed in case there was no previous discussion or issues. (This doesn't apply to typos!)
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• I've updated the documentation accordingly.
• I ran dev/reformat(backend) and cd web && npx lint-staged(frontend) to appease the lint gods

[Copilot]

Copilot reviewed 1 out of 1 changed files in this pull request and generated no comments.

Comments suppressed due to low confidence (1)

api/services/dataset_service.py:2028

• If max_position can be 0 as a valid value, consider explicitly checking for None (e.g., 'if max_position is not None') rather than relying on the falsy evaluation. This helps avoid unintended behavior when 0 is a valid position.

position=max_position + 1 if max_position else 1,