Summary:
In browser where user is logged in multiple times, she can start
creating a new site from docs org where user B is the default one, and end up on the
api endpoint where user A is the default one. This resulted in wrong userId in the handler.
Test Plan: New test
Reviewers: georgegevoian
Reviewed By: georgegevoian
Differential Revision: https://phab.getgrist.com/D4029