#1457: Improved detection of empty sortable

Author: owen-m1

Sortable.js

@@ -175,7 +175,7 @@
 		 */
 		_detectNearestEmptySortable = function(x, y) {
 			for (var i = 0; i < sortables.length; i++) {
-				if (sortables[i].children.length) continue;
+				if (_lastChild(sortables[i])) continue;
 
 				var rect = _getRect(sortables[i]),
 					threshold = sortables[i][expando].options.emptyInsertThreshold,
@@ -1224,12 +1224,12 @@
 					return completed();
 				}
 
-				if ((el.children.length === 0) || (el.children[0] === ghostEl) ||
-					_ghostIsLast(evt, axis, el) && !dragEl.animated
-				) {
-					//assign target only if condition is true
-					if (el.children.length !== 0 && el.children[0] !== ghostEl && el === evt.target) {
-						target = _lastChild(el);
+				var elLastChild = _lastChild(el);
+
+				if (!elLastChild || _ghostIsLast(evt, axis, el) && !elLastChild.animated) {
+					// assign target only if condition is true
+					if (elLastChild && el === evt.target) {
+						target = elLastChild;
 					}
 
 					if (target) {
@@ -1986,10 +1986,8 @@
 	function _lastChild(el) {
 		var last = el.lastElementChild;
 
-		while (last === ghostEl || last.style.display === 'none') {
+		while (last && (last === ghostEl || last.style.display === 'none')) {
 			last = last.previousElementSibling;
-
-			if (!last) break;
 		}
 
 		return last || null;