GT Crashes when inspecting remote HEAD branches

[refactoringdr]

To recreate:

1. Open the git tool and select a repository.
2. Go to the commits tab and double-click to inspect a commit
3. Select the Raw inspector on the commit and double-click the repository slot to inspect it
4. Select the Remotes tab on the repository inspect, which will list all the remotes
5. Double-click the HEAD remote branch
6. CRASH

I believe the problem is that HEAD isn't a true remote branch but a pointer to one of the other branches and this is causing an illegal FFI call to libgit