recent_topics_ui: Extend check for unread to PMs.
recent_topics_ui: Extend check for unread to PMs.

Since we also have PMs now, `has_unread` should consider that case
too. This seems like a good change regardless.

zulip/zulip,zulip/zulip,zulip/zulip,zulip/zulip,zulip/zulip,zulip/zulip,zulip/zulip