[lib] Check if device list exists instead of using userHasDeviceList() in useUsersSupportThickThreads()

Summary:
https://linear.app/comm/issue/ENG-9509/accepting-a-friend-request-on-web-creates-thin-thread

Related discussion: https://phab.comm.dev/D13939#389720

Depends on D13938

Test Plan: Send and accept a friend request. Verify that a thick thread is created.

Reviewers: kamil, tomek

Reviewed By: kamil

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D14022