Don't try to load profile images for projects with no profile image
Summary: Ref T8631. Projects may not have a profile image PHID; don't try to load it if they don't.
Test Plan: Saw WHERE phid IN ('') query stop happening on a local feed story page.
Reviewed By: btrahan
Maniphest Tasks: T8631
Differential Revision: https://secure.phabricator.com/D13476