`edit-readme` button is misplaced, when readme contains no headings #4269

Screenshot:

I think the edit button with the pencil icon should be in the top right.

Example pages where the bug manifests:

• https://github.com/theam/aws-lambda-haskell-runtime
• https://github.com/ThomasTerp/LunkyBox

Example where everything is fine, despite the document not starting with a heading: https://github.com/scottrogowski/mongita (Presumably OK because the document contains headings later on.)

Reproduces in FF and Chrome. Extension version 21.4.13.

Probably related to https://github.com/sindresorhus/refined-github/issues/4157.