[keyserver] Fetch primary links only when a user is logged in
Summary:
Calling userID getter on Viewer results in an exception when a user isn't logged in. A logged out user shouldn't have access to invite links, so we can return an empty array for them.
Test Plan: Open web app as a logged out user and check if it loads correctly. Log in and check if the links are fetched.
Reviewers: kamil, inka, michal, ashoat
Reviewed By: ashoat
Subscribers: ashoat
Differential Revision: https://phab.comm.dev/D8329