[web-db] avoid database init on app start on Safari

Summary:
In general, we establish database connection immediately after app start, on Safari we need to wait for encryption key generated from main thread.
(context)

Depends on D8123

Test Plan: Database should be inited from sqlite-data-handler.js

Reviewers: michal, tomek

Reviewed By: tomek

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D8124