Fix phid accumulation for handles

Summary: I goofed this, $phids was already being populated and I changed the
meaning. This causes a fatal if you filter the list by a user who is not an
author or first reviewer for any of the revisions (e.g., no open revisions).

Test Plan: Looked at the list of a user with no revisions.

Reviewers: codeblock, jungejason

Reviewed By: codeblock

CC: aran, codeblock, jungejason

Differential Revision: 989