Merge pull request #29 from lazd/issue28

* fixed #28

Sortable.js

@@ -187,6 +187,7 @@
 					, i = touchDragOverListeners.length
 				;
 
+				if( parent ){
 					do {
 						if( parent[expando] === group ){
 							while( i-- ){
@@ -203,6 +204,7 @@
 						target = parent; // store last element
 					}
 					while( parent = parent.parentNode );
+				}
 
 				_css(ghostEl, 'display', '');
 			}