Push from detached head not possible when no local branch exists

What steps will reproduce the problem?

1. Checkout Detached Head
2. Delete all local branches
3. Open Push Dialog (e.g. shift + right-click in Log)
4. Fill valid values for Local and Remote Branch (e.g. commit-hash)
5. OK not active

What is the expected output? What do you see instead?

OK is active and can be clicked

What version of TortoiseGit and Git are you using? On what operating system?

TortoiseGit 2.6.0.0 git version 2.8.1.windows.1