Comparison download format misses rows for unfilled areas with expectation

When you choose the "comparison" download format, every area with an expectation should be included in the output, even if a participant did not fill that area. Instead, the output currently only includes filled areas with an expectation. It is likely that this omission is due to a mistake in the query.

Inspect the comparison download entry point and the query that selects areas with expectations. Reproduce the case where a participant leaves an expected area unfilled, then verify that the comparison output includes that area as well as filled areas.

Written by the indexing model from the issue text.