fix(rfc2136): Use correct index for accessing UpdateOld if there are multiple chunks

[schwajo]

If there are many updates to be made, UpdateNew is split into several chunks.

To get the corresponding row in UpdateOld, only the index in the current chunk is used.
But UpdateOld is not splitted, to get the right element in UpdateOld (not splitted), you have to adjust the index to be in the corresponding chunk.

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• Yes, this PR title follows Conventional Commits
• Yes, I added unit tests
• Yes, I updated end user documentation accordingly

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• ✅ login: schwajo (a7786a5)

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[mloiseleur]

@schwajo You need to sign the CLA before we can review this PR.

[ivankatliarchuk]

/ok-to-test

[ivankatliarchuk]

/lgtm

[mloiseleur]

@joshlreese @Jeremy-Boyle Wdyt of this PR ? Do you think you can review it ?

[mloiseleur]

/lgtm
/approve

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