[web] Include current pending thread in thread list

Summary: Currently opened pending thread hasn't been displayed in thread list (only pending sidebar was included). This change includes it in the list (similar to pending sidebar).

Test Plan: Create new pending thread (e.g. by opening empty thread with non-friend). It should be displayed on the top of the thread list.

Reviewers: tomek, atul, abosh

Reviewed By: tomek

Subscribers: ashoat, adrian, abosh

Differential Revision: https://phab.comm.dev/D4456