jQuery tabs code not checking

So the tabs code is always running even when the wpseo metabox isn't
shown. This just checks to see if the tabs screen is displayed before
checking the hash or default. If other metabox use tabs this won't mess
with them.
Merge pull request #352 from imageinabox/master

jQuery tabs code only working when it's actually WPSEO's tab in a metabox. Props @imageinabox.