Only change label if we have a label for that status

Addresses http://bugsnag.com/edx-jira-webhooks/openedx-webhooks/errors/5435779f94b7f2cb64824fc7?event_id=5435779fe87503d63622961d

Developing with out tests is really fun it's like being in the wild west :smile: 

:cactus: :cow: :horse: :horse_racing: :cactus: