Opening config produces Errno 22

### Problem

Trying to open the config file on Windows 10 with ``beet -vv config -e`` leads to ``error: Could not edit configuration: [Errno 22] Invalid argument``. Checked the file and it exists and would be open with Notepad++.

### Setup

* OS: Windows 10
* Python version: Python 3.6 (Python 2.7 is installed to put not used by default)
* beets version: 1.4.6
* Turning off plugins made problem go away (yes/no): don't have any

My configuration (output of `beet config`) is:

```yaml
{}
```

Start by reproducing `beet -vv config -e` on Windows 10 with the reported Python and beets versions, using the empty configuration shown. Read the implementation behind the `config -e` CLI entry point and trace how the editor is launched; done means the existing configuration opens successfully without Errno 22.

Written by the indexing model from the issue text.