Fix the preupdate hook so that it works when the "old.*" row has a column with a non-NULL default value that was added by ALTER TABLE ADD COLUMN after the current record was created. (tags: preupdate-hook-fix)

Fix the preupdate hook so that it works when the "old.*" row has a column with a non-NULL default value that was added by ALTER TABLE ADD COLUMN after the current record was created. (tags: preupdate-hook-fix)