set frontier_log to last log that decodes and break

[4meta5]

closes #217

What important points reviewers should know?

initial suggestion

The previous loop set frontier_log to the last log that is_some (after a try_to decode attempt) in notification.header.digest.logs. If there are no logs that are is_some, then it is None.

The new loop starts from the end and goes backwards; it sets frontier_log to the last log that is_some and then breaks from the loop instead of going over all the logs every time. Worst case is still the same, but, if not worst case, this is better because it breaks early.

Checklist

This is a small change to how the logic is expressed, but doesn't change the underlying logic.

• No purge of network required
• No version bumps required
• No changes to docs