R1:c6fd969416a5

Fix an edge case when trying to pull duplicate refs via Doorkeeper

Summary:
Report from Asana. In some unclear circumstances, we my attempt to resolve duplicate refs which currently ends up hitting a duplicate key error.

Instead, reference the same external object if we happen to be handed duplicate refs.

Test Plan:
Used this script to reproduce the issue. Applied the fix; issue went away:

#!/usr/bin/env php
<?php

require_once 'scripts/__init_script__.php';

$args = new PhutilArgumentParser…