Make resilient against events on PR in incorrect state

Ensure things don't go wrong if someone manages to execute unexpected events, e.g. the "Reset" button when the PR is merging or already merged. Could happen if event is triggered on an old commit

Start by tracing the event handling for the "Reset" action and the pull request merging and merged states. Reproduce or inspect how an event from an old commit is processed. Done means unexpected events do not cause incorrect behavior when the pull request is merging or already merged.

Written by the indexing model from the issue text.