fix: Negative time duration for labels applied after issue close; Inflated metric numbers for unlabeled labels on open issues

[smstone]

Pull Request

I came across two additional issues in label time durations:

1. Negative time durations metrics for issues where the label was applied after issue close.
2. Inflated time durations for unlabeled issues where the issue is still open (I think I introduced the issue in fix: Negative time reported for "time label applied" measurement #283)

Proposed Changes

Readiness Checklist

Author/Contributor

• If documentation is needed for this change, has that been included in this pull request
• run make lint and fix any issues that you have introduced
• run make test and ensure you have test coverage for the lines you are introducing

Reviewer

• Label as either fix, documentation, enhancement, infrastructure, maintenance, or breaking

[jmeridth]

@smstone another great catch. Will look soon. Thank you for the contribution.

[jmeridth]

Tested. Looks good. Thank you @smstone.