This becomes especially bad in this query from /api/v4/projects
endpoint:

```
SELECT COUNT(*)
FROM
  (SELECT 1 AS one
   FROM "projects"
   WHERE (EXISTS
            (SELECT 1
             FROM "project_authorizations"
             WHERE "project_authorizations"."user_id" = 1
               AND (project_authorizations.project_id = projects.id)
            )
            OR projects.visibility_level IN (10,20)
          )
     AND "projects"."visibility_level" = 0
     AND "projects"."pending_delete" = FALSE
   LIMIT 10001) subquery_for_count
```

Note we attempt to limit the damage with `LIMIT 10001` but Postgres
keeps trying to find any row that will match the impossible visiblity
level combination of (10,20) & (0), which goes way beyond 10001 rows.

So we omit the OR in the case where we encounter a visibility level
set which is null.