[8.14](backport #39404) Add error check to groupToEvents so we don't blindly add error values

[mergify]

Proposed commit message

fixes #38140

This adds an error check to the eventMap in groupToEvents() so we don't report an error where there isn't one.

I almost never touch any of the windows code, so feel free to ignore this until CI is green.

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works
• I have added an entry in CHANGELOG.next.asciidoc or CHANGELOG-developer.next.asciidoc.

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This is an automatic backport of pull request #39404 done by [Mergify](https://mergify.com).

[elasticmachine]

Pinging @elastic/elastic-agent-data-plane (Team:Elastic-Agent-Data-Plane)

[mergify]

This pull request has not been merged yet. Could you please review and merge it @fearful-symmetry? 🙏

[mergify]

This pull request is now in conflicts. Could you fix it? 🙏
To fixup this pull request, you can check out it locally. See documentation: https://help.github.com/articles/checking-out-pull-requests-locally/

git fetch upstream
git checkout -b mergify/bp/8.14/pr-39404 upstream/mergify/bp/8.14/pr-39404
git merge upstream/8.14
git push upstream mergify/bp/8.14/pr-39404