ICU-22723 Add line number info to icuexportdata handleError

[mihnita]

Checklist

• Required: Issue filed: https://unicode-org.atlassian.net/browse/ICU-22723
• Required: The PR title must be prefixed with a JIRA Issue number.
• Required: The PR description must include the link to the Jira Issue, for example by completing the URL in the first checklist item
• Required: Each commit message must be prefixed with a JIRA Issue number.
• Issue accepted (done by Technical Committee after discussion)
• Tests included, if applicable
• API docs and/or User Guide docs changed or added, if applicable

[mihnita]

Small "quality of life improvement"
We talked about it.

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And I hope using ICU-22723 for small cleanup changes like these is OK.
See comments on PR #3001

mihnita: I hope that the issues is OK (ICU-22723: "ICU 76rc BRS")
markusicu: rc BRS ticket is fine

If not, I think it would be nice to have a general "catch-all" issue for small code improvements.
Similar to ICU-22722 "ICU 76 docs minor fixes".
Reviewers can always ask for a separate issue if they think that the change does not qualify as "minor fix"

[jira-pull-request-webhook]

Hooray! The files in the branch are the same across the force-push. 😃

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