Diffusion - be sure to properly unserialize result from conduit query

Summary: Fixes T7256.

Test Plan: Looked at rXPRF0a7a5f69f5d7 in a local instance. things looked great both pre and post patch.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin, epriestley

Maniphest Tasks: T7256

Differential Revision: https://secure.phabricator.com/D11790