Support package_data with empty key and multiple values

[hugovk]

Given setup.py:

from setuptools import setup

setup(package_data={"": ["LICENSE", "NOTICE"]})

Run:

$ setup-py-upgrade .
./setup.py and ./setup.cfg written!

Produces setup.cfg:

[options.package_data]
 =
    LICENSE
    NOTICE

Expected:

[options.package_data]
* =
    LICENSE
    NOTICE

---

This is similar to #4 (fixed by PR #5), and the simple case still works; this setup.py:

from setuptools import setup

setup(package_data={"": ["LICENSE"]})

Correctly produces this setup.cfg:

[options.package_data]
* =
    LICENSE

[asottile]

actually on second thought, I think package_data={'': ...} should be rejected outright

it doesn't appear to work, and even if it did it would pollute the top level with data files

[hugovk]

Ah yes, I'm using setuptools_scm anyway so looks like I don't need package_data at all.

[asottile]

but it does look like the if statement should be moved -- cc @mxr