Moving a topic does not correctly set latest post for forum

Just in case anyone else spots this, I've put this here for now as a reminder for myself to fix this.

Steps to reproduce:

1. Create a Topic
2. Reply to the topic
3. Move the topic to a different forum
4. Observe that the forum takes the first post instead of the last post related to the topic

This is not a consistent issue and only happens when:

• The topic is newer than other posts in the target forum
• When there is an updated reply in the topic that is newer than the latest post in that topic