Infinite loop with empty CSS string

[yunosh]

Since upgrading to the latest 7.x version (from a pre-6.0-snapshot), there is some infinite loop in the code if you pass an empty string to the parser

$settings = Sabberworm\CSS\Settings::create();
$settings->withMultibyteSupport(false);
$parser = new Sabberworm\CSS\Parser('', $settings);
$parser->parse();