[web] [fix] give chat thread list breadCrumbs height

Summary:
chat thread arrow layout is broken without breadcrumbs. If there isn't a parent thread, will just default to the thread name to not break the UI.

ios:

https://linear.app/comm/issue/ENG-809/thread-arrows-are-not-aligned-correctly

Test Plan: arrow shouldn't loose it position if there isn't a parnet element. You can patch the code and toggle the conditional to see that the arrows layout never breaks.

Reviewers: ashoat, atul

Reviewed By: ashoat, atul

Subscribers: atul, ashoat, palys-swm, Adrian, karol-bisztyga

Differential Revision: https://phabricator.ashoat.com/D3328