Fix crash of 'swh lister run' when called without -l

before:

$ 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']

after:

$ swh lister run
Usage: swh lister run [OPTIONS] [OPTIONS]...
Try 'swh lister run -h' for help.

Error: Missing option '--lister' / '-l'. Choose from:
	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