Fix two problems with actor order in Asana bridge

Summary: We attempt to choose the most reasonable actor when synchronizing to Asana, but Asana is seeing the sync choose a less-reasonable actor. I spotted two places where the order may get disrupted; make sure we retain order. This is somewhat tricky to repro locally (it depends on things like native account order) but I think this is the right fix. If not, I'll add more logging. Ref T2852.

Test Plan: Used `bin/feed republish` to sync Asana events.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T2852

Differential Revision: https://secure.phabricator.com/D6443