Fix D2490 (make macro handler correctly bail if there are no macros)

Summary: D2490 was not my finest hour and I incorrectly thought it was a null value from error. In reality this error is impossible and its just a valid empty array so instead use the empty predicate to bail.

Test Plan: with our logic combined, this be tested

Reviewers: vrana, epriestley

Reviewed By: epriestley

CC: aran, Koolvin

Differential Revision: https://secure.phabricator.com/D2503