[lib] Mark missing users when fetching device lists

Summary: issue: ENG-9631

Test Plan:
Tested that when a user is missing a device list the accountMissingStatus is set. Checked that lastChecked is updated with next requests but missingSince stays the same.

checked that if non-empty a device list is returned by identity, accountMissingStatus is removed.

Reviewers: tomek, kamil

Reviewed By: tomek

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D13728