[ML] Fix Anomaly Explorer population charts when multiple causes in anomaly

[peteharverson]

Summary

Fixes the anomaly charts in the Anomaly Explorer for anomalies in population detectors with by and over fields when there are multiple items in the anomaly record causes array.

Previously the charts for anomalies with multiples causes would render blank:

After:

This bug was introduced by #67569 as the calculation used to set the y axis domain would set the min and max to NaN as the actual and typical values are not present in the top level of the anomaly record used for the chart data for anomalies with more than one item in the causes array.

Checklist

• This was checked for cross-browser compatibility

Fixes #83676

[elasticmachine]

Pinging @elastic/ml-ui (:ml)

[kibanamachine]

💚 Build Succeeded

• continuous-integration/kibana-ci/pull-request
• Commit: ef7db6a

Metrics [docs]

Async chunks

Total size of all lazy-loaded chunks that will be downloaded as the user navigates the app

id	before	after	diff
ml	5.2MB	5.2MB	+25.0B

To update your PR or re-run it, just comment with:
@elasticmachine merge upstream

[walterra]

LGTM, also did a local test to verify charts are populated.