[web] Render ChatMessageList only if activeChatThreadID exists

Summary:
Fix for issue: https://linear.app/comm/issue/ENG-1489/web-app-was-not-loading-properly-error-with-chatmessagelistcontainer
Moved activeChatThreadID selector one level higher in components tree to conditionally render ChatMessageListContainer and avoid need to further modifications inside, as the component was designed with assumption that activeChatThreadID always exists.

Test Plan: Register new user in app. Don't enter any thread on mobile. After opening chat in web app, the issue described in Linear task no longer appears.

Reviewers: tomek, atul, abosh

Reviewed By: tomek, abosh

Subscribers: ashoat, adrian

Differential Revision: https://phab.comm.dev/D4692