Improve performance by excluding 0 results

When running wiki cohorts, these three metrics were returning
editor_id: 0 for editors that passed early filters but did not pass the
ultimate metric test.  This is inefficient for a few reasons, so I
cleaned up the tests that expected this behavior and fixed the code.

Change-Id: I280028ee85b8e97da8ea09b34012654c49c12c9f
Merge "Improve performance by excluding 0 results"