Threaded view does not indicate unread messages

[gtandersen]

Describe the bug When using the threaded view and one of older messages is unread, the conversation does not indicate having an unread email.

To Reproduce Steps to reproduce the behavior:

1. Go to https://runbox.com/app
2. Enable threaded view (with local index) where the most recent message is read, and others are unread
3. Observe that there is no indication there are unread messages in the thread

Expected behavior There should be an indication there are unread messages in the thread.