Fix for Phragment ZIP controller
Summary: This applies a minor fix for the Phragment ZIP controller where it would raise missing index errors when attempting to map deleted fragments to file PHIDs (since deleted fragments no longer have files).
Test Plan: Tested this patch on a live server and saw the issue go away.
Reviewers: epriestley, #blessed_reviewers
Reviewed By: epriestley
CC: Korvin, epriestley, aran
Differential Revision: https://secure.phabricator.com/D8243