solaar-cli: fix argument parsing in Python 3 again

Fix from e3a887f36c, this got removed
in:

    commit 3b75b69970
    Author: Daniel Pavel <daniel.pavel@gmail.com>
    Date:   Fri Aug 9 12:25:47 2013 +0200

        merged solaar-cli functionality into main solaar binary

lib/solaar/cli/__init__.py

@@ -136,6 +136,12 @@ def run(cli_args=None):
 		args = _cli_parser.parse_args(cli_args)
 	else:
 		args = _cli_parser.parse_args()
+		# Python 3 has an undocumented 'feature' that breaks parsing empty args
+		# http://bugs.python.org/issue16308
+		if not 'cmd' in args:
+			_cli_parser.print_usage(_sys.stderr)
+			_sys.stderr.write('%s: error: too few arguments\n' % NAME.lower())
+			_sys.exit(2)
 		action = args.action
 	assert action in actions