I'm trying to redirect users from an existing path in Drupal 7 to another existing path. I want to implement the following rule:

<code>comment/reply/123</code> should redirect to <code>node/123#comment-form</code>

But

<code>comment/reply/123/456</code> should NOT redirect anywhere and just go where it goes.

I've tried to implement this behavior with hook_menu(), but here's the problem. When I register an item with the path <code>'comment/reply/%'</code> that corresponds to <code>comment/reply/123</code>, it automatically includes paths like <code>comment/reply/123/456</code>. I know that's intended and changed my code to include this case, but can't figure out how to redirect users only when they hit <code>comment/reply/123</code>. Here's my code:

<pre><code>
function mymodule_menu()
{
    $items = array();
    $items['comment/reply/%/%'] = array(
        'title' => 'bla',
        'page callback' => '_mymodule_redirect',
        'page arguments' => array(0, 1),
        'access callback' => TRUE,
        'type' => MENU_CALLBACK,
    );
    return $items;
}

function _mymodule_redirect($node_id, $comment_id)
{
	if(isset($comment_id))
	{
		return; //I want to just go to comment/reply/123/456 here, but it gives me a blank page
	}
	else
	{
		drupal_goto('node/' . $node_id . '#comment-form');
	}
}
</code></pre>

So how do I go where I want to go?