Diffusion - fix bug from D5883
Summary: forgot to specify the commit! On github as https://github.com/facebook/phabricator/pull/318, though this is a tighter fix.
Test Plan: tried to save an owners package with a folder - FAIL - then with the patch - GREAT SUCCESS
Reviewers: epriestley
Reviewed By: epriestley
CC: aran, Korvin
Differential Revision: https://secure.phabricator.com/D5933