In 2011, column-store files were changed to support physical extension (see commit 2f5ab0b9c47885cbd29aa00028be8f0f64bf4cb2). As part of that commit, the column-store code was changed to treat a WT_COL page offset of 0 as a deleted cell, so an array of cleared memory would appear as a set of deleted records.

That feature was removed in a few months in favor of skiplist inserts (see commit bae4cd52b0b72100714104eb2895b779783dcb5a), but the code to check for a WT_COL page offset of 0 was left in place.

I believe it can be removed.