Basic Export creates invalid CSVs when no ratings exist

[sstults]

Describe the bug
CSV readers throw an error when the header line specifies a number of columns but all records do not have that number of columns.

To Reproduce
Steps to reproduce the behavior:

1. Go to a Case where some queries have not been rated
2. Click on Export
3. Scroll down to Basic
4. Click Export
5. Examine the CSV: Entries that have no ratings do not supply the correct number of commas (2)

Expected behavior
If a query doesn't have ratings it should either be skipped altogether or empty columns added. For example, a query for "foo" would look like this:

query,docid,rating
foo,,

The way it works now is:

query,docid,rating
foo

Screenshots
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Additional context
Add any other context about the problem here.

[epugh]

Hey @sstults what about

query,docid,rating
foo, , 

[epugh]

Never mind, I got it to:

query,docid,rating
foo,,