Zend_View_Helper_HeadLink notice using compact()

[AntoineMarques]

When using Zend_View_Helper_HeadLink to append a stylesheet as the documentation says a notice is thrown.
This is due to extras being undefined when calling compact on line 393.

Reproduce

class HeadLinkTest extends \PHPUnit\Framework\TestCase
{
    public function test() 
    {
        $this->expectException(\PHPUnit\Framework\Error\Notice::class);

        $helper = new \Zend_View_Helper_HeadLink();
        $helper->appendStylesheet('foo.css');
    }
}