Fix crash of 'swh lister run' when called without -l
```
$ swh lister run
Traceback (most recent call last):
File "/home/dev/.local/bin/swh", line 33, in <module>
sys.exit(load_entry_point('swh.core', 'console_scripts', 'swh')())
File "/home/dev/swh-environment/swh-core/swh/core/cli/__init__.py", line 144, in main
return swh(auto_envvar_prefix="SWH")
File "/home/dev/.local/lib/python3.9/site-packages/click/core.py", line 1130, in __call__
return self.main(*args, **kwargs)
File "/home/dev/.local/lib/python3.9/site-packages/click/core.py", line 1055, in main
rv = self.invoke(ctx)
File "/home/dev/.local/lib/python3.9/site-packages/click/core.py", line 1657, in invoke
return _process_result(sub_ctx.command.invoke(sub_ctx))
File "/home/dev/.local/lib/python3.9/site-packages/click/core.py", line 1657, in invoke
return _process_result(sub_ctx.command.invoke(sub_ctx))
File "/home/dev/.local/lib/python3.9/site-packages/click/core.py", line 1404, in invoke
return ctx.invoke(self.callback, **ctx.params)
File "/home/dev/.local/lib/python3.9/site-packages/click/core.py", line 760, in invoke
return __callback(*args, **kwargs)
File "/home/dev/.local/lib/python3.9/site-packages/click/decorators.py", line 26, in new_func
return f(get_current_context(), *args, **kwargs)
File "/home/dev/swh-environment/swh-lister/swh/lister/cli.py", line 68, in run
get_lister(lister, **config).run()
File "/home/dev/swh-environment/swh-lister/swh/lister/__init__.py", line 75, in get_lister
raise ValueError(
ValueError: Invalid lister None: only supported listers are ['arch', 'aur', 'bitbucket', 'bower', 'cgit', 'conda', 'cpan', 'cran', 'crates', 'debian', 'fedora', 'gitea', 'github', 'gitlab', 'gnu', 'gogs', 'golang', 'hackage', 'hex', 'launchpad', 'maven', 'nixguix', 'npm', 'nuget', 'opam', 'packagist', 'phabricator', 'pubdev', 'puppet', 'pypi', 'rubygems', 'sourceforge', 'tuleap']
```
596e8c6c40