Summary:
This brings the treatment of metadata updates being broadcast to a user
into line with how it is treated when they first open the document.
Specifically, this fixes a bug where, for a document with a default access
rule denying access to everything, a user would not receive any
metadata updates.
Test Plan: added test; existing tests pass
Reviewers: jarek, dsagal
Reviewed By: jarek, dsagal
Differential Revision: https://phab.getgrist.com/D3711