R1:56838c0e3dc2

Fix an issue where querying for a large number of projects by slug could paginate incorrectly

Summary:
See PHI1809. This query may join the "slug" table, but each project may have multiple slugs, and the query does not "GROUP BY" when this join occurs.

This may lead to partial result sets and unusual paging behavior.

This could likely be caught categorically in `loadAllFromArray()`; I'll adjust this in a followup.

Test Plan:
A minimal reproduction case is something like:

- Give project P slugs: a, b…