[Bug] Error when trying to unstage files in fresh repo

[Piolie]

Steps to reproduce

1. Create a new empty file: file.txt.
2. Initialize a new git repository: git init.
3. Add file to the index: git add *.
4. Open sourceGit, select the file and unstage it, either using Space/Enter or with the arrow button.

Expected Behavior

The file is unstaged.

Actual Behavior

The following error is generated:

fatal: ambiguous argument 'HEAD': unknown revision or path not in the working tree.
Use '--' to separate paths from revisions, like this:
'git <command> [<revision>...] -- [<file>...]'

[love-linger]

Fixed.