Determine the correct target before onFilter

Fix #156 and also returning correct indexes if a drag handle is present (#154).

README.md

@@ -86,6 +86,7 @@ var sortable = new Sortable(el, {
 		// same properties as onUpdate
 	},
 
+	// Attempt to drag a filtered element
 	onFilter: function (/**Event*/evt) {
 		var itemEl = evt.item;  // HTMLElement receiving the `mousedown|tapstart` event.
 	}

Sortable.js

@@ -166,17 +166,23 @@
 				el = this.el,
 				filter = options.filter;
 
-			// get the index of the dragged element within its parent
-			startIndex = _index(target);
-
 			if (evt.type === 'mousedown' && evt.button !== 0 || options.disabled) {
 				return; // only left button or enabled
 			}
 
+			if (options.handle) {
+				target = _closest(target, options.handle, el);
+			}
+
+			target = _closest(target, options.draggable, el);
+
+			// get the index of the dragged element within its parent
+			startIndex = _index(target);
+
 			// Check filter
 			if (typeof filter === 'function') {
 				if (filter.call(this, target, this)) {
-					_dispatchEvent(el, 'filter', target);
+					_dispatchEvent(el, 'filter', target, undefined, startIndex);
 					return; // cancel dnd
 				}
 			}
@@ -186,17 +192,11 @@
 				});
 
 				if (filter.length) {
-					_dispatchEvent(el, 'filter', target);
+					_dispatchEvent(el, 'filter', target, undefined, startIndex);
 					return; // cancel dnd
 				}
 			}
 
-			if (options.handle) {
-				target = _closest(target, options.handle, el);
-			}
-
-			target = _closest(target, options.draggable, el);
-
 			// IE 9 Support
 			if (target && evt.type == 'selectstart') {
 				if (target.tagName != 'A' && target.tagName != 'IMG') {