Properly resets firingLength when emptying the list. Fixes #13517

src/callbacks.js

@@ -145,6 +145,7 @@ jQuery.Callbacks = function( options ) {
 			// Remove all callbacks from the list
 			empty: function() {
 				list = [];
+				firingLength = 0;
 				return this;
 			},
 			// Have the list do nothing anymore