The common close_all_review_requests() function for close-submitted

hooks attempted to log any review request IDs referenced in commits that

couldn't be found in the database. Part of this involved building a map

of the ones that could be found, but the code to do this was broken,

causing a crash.
This change fixes the crash, and adds new unit tests for the affected

services that verify things work correctly when encountering missing

review request IDs.

Unit tests pass.