Subject of the issue

HEAD detached... shows as a local branch (in g.branches.local)

Your environment

• version of git and ruby-git: latest
• version of ruby: latest

Steps to reproduce

• go to a git repo dir
• get in a "HEAD detached" state
• Git.open('.').branches.local.map(&:gcommit).map &:message

Expected behaviour

list commit messages of local branches

Actual behaviour

Git::GitExecuteError (git '--git-dir=.../.git' '--work-tree=...' '-c' 'color.ui=false' cat-file 'commit' '(HEAD detached at ...)' 2>&1:fatal: Not a valid object name (HEAD detached at ...))