Issue when forking a repo that's already forked in an organization user is part of

[tbroadley]

Case study: I'm part of the Boltmade org, which has a fork of DefinitelyTyped. When I ran github-spellcheck on DefinitelyTyped, the tool wanted to fork it to tbroadley/DefinitelyTyped, but actually didn't because the Boltmade fork existed. Then the clone from tbroadley/DefinitelyTyped failed.