editor.formatOnSave prevents onWillSaveTextDocument from firing

- VSCode Version: 1.19.2
- OS Version: Windows 10 Pro

Steps to Reproduce:

1. `"editor.formatOnSave": true`
2. Open a file that has no formatting (e.g., README.md).
3. Modify the file.
4. Hit save. `onWillSaveTextDocument` is never hit.

@jrieken, you might be interested in this!

See also: https://github.com/editorconfig/editorconfig-vscode/issues/183
