fixed an issue when data-lightbox parameter only consists of numbers

Author: fritzmg

system/modules/magnific_popup/assets/init-magnific-popup.js

@@ -37,7 +37,7 @@ function initMagnificPopup( options )
 		var $group = $('a[data-lightbox="'+group+'"]');
 
 		// parse the group name
-		var names = group.split(' ');
+		var names = group.toString().split(' ');
 		var width = null;
 		var height = null;
 		$.each( names, function( index, name )