Twenty Fourteen: Avoid passing an empty string to document.getElementById().

props nabil_kadimi.
fixes #28340.

git-svn-id: https://develop.svn.wordpress.org/trunk@28598 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-content/themes/twentyfourteen/js/functions.js

@@ -40,7 +40,13 @@
 	 * @link http://www.nczonline.net/blog/2013/01/15/fixing-skip-to-content-links/
 	 */
 	_window.on( 'hashchange.twentyfourteen', function() {
-		var element = document.getElementById( location.hash.substring( 1 ) );
+		var hash = location.hash.substring( 1 ), element;
+
+		if ( ! hash ) {
+			return;
+		}
+
+		element = document.getElementById( hash );
 
 		if ( element ) {
 			if ( ! /^(?:a|select|input|button|textarea)$/i.test( element.tagName ) ) {