Broken diff view for commit with rename only #2374

Without Refined GitHub:

<img width="1035" alt="without" src="https://user-images.githubusercontent.com/873258/63514645-55f42b00-c4e9-11e9-8fb9-b4382ec70cdd.png">

With Refined GitHub:

<img width="1016" alt="with" src="https://user-images.githubusercontent.com/873258/63514666-5f7d9300-c4e9-11e9-880d-befb6aab0ede.png">

URL: https://github.com/mozilla/addons-server/pull/12182/files/353b86e8f6c40892169aa1947ae211bd315ec846..05f43fb44923b21b7e9b7c4d963dea2f95d2d95a