Fix WP Admin menu items no longer clickable

... when on WPSEO pages as reported in [issue #733](https://github.com/Yoast/wordpress-seo/issues/733) and [#738](https://github.com/Yoast/wordpress-seo/issues/738)

Caused by commit b19f0ea4bbb6248a4cfe3940ff74856e218fd323