Avoid KeyError with --no-setuptools

Mathieu Parentrequested to merge
no_setuptools_keyerror into master

To fix:

# virtualenv --no-setuptools venv  --with-traceback
Traceback (most recent call last):
  File "/usr/bin/virtualenv", line 33, in <module>
    sys.exit(load_entry_point('virtualenv==20.4.0+ds', 'console_scripts', 'virtualenv')())
  File "/usr/lib/python3/dist-packages/virtualenv/__main__.py", line 65, in run_with_catch
    run(args, options, env)
  File "/usr/lib/python3/dist-packages/virtualenv/__main__.py", line 18, in run
    session = cli_run(args, options, env)
  File "/usr/lib/python3/dist-packages/virtualenv/run/__init__.py", line 32, in cli_run
    of_session.run()
  File "/usr/lib/python3/dist-packages/virtualenv/run/session.py", line 47, in run
    self._seed()
  File "/usr/lib/python3/dist-packages/virtualenv/run/session.py", line 60, in _seed
    self.seeder.run(self.creator)
  File "/usr/lib/python3/dist-packages/virtualenv/seed/embed/via_app_data/via_app_data.py", line 43, in run
    with self._get_seed_wheels(creator) as name_to_whl:
  File "/usr/lib/python3.9/contextlib.py", line 117, in __enter__
    return next(self.gen)
  File "/usr/lib/python3/dist-packages/virtualenv/seed/embed/via_app_data/via_app_data.py", line 130, in _get_seed_wheels
    if name_to_whl['setuptools'].path.is_relative_to(BUNDLE_FOLDER):
KeyError: 'setuptools'

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