[lib] Fix crash when logged out with sidebar open

Summary: See more details about the crash in ENG-3837. The inline code comment also provides more context on what was happening.

Test Plan: I reproduced the crash described in the Linear issue, and then confirmed it no longer occurs with this change

Reviewers: michal, tomek, atul

Reviewed By: atul

Differential Revision: https://phab.comm.dev/D7719