Summary:
Skipping columns during incremental imports wasn't working for certain
column types, such as numeric columns. The column's default value was
being used instead (e.g. 0), overwriting values in the destination
table.
Test Plan: Browser tests.
Reviewers: jarek
Reviewed By: jarek
Subscribers: alexmojaki
Differential Revision: https://phab.getgrist.com/D3402