Model.update optimization. Dropped 1% from Washington DC profile sinc…

…e it no longer sets the array length to zero

Source/Scene/ModelAnimationCollection.js

@@ -330,6 +330,15 @@ define([
      * @private
      */
     ModelAnimationCollection.prototype.update = function(frameState) {
+        var scheduledAnimations = this._scheduledAnimations;
+        var length = scheduledAnimations.length;
+
+        if (length === 0) {
+            // No animations - quick return for performance
+            this._previousTime = undefined;
+            return false;
+        }
+
         if (JulianDate.equals(frameState.time, this._previousTime)) {
             // Animations are currently only time-dependent so do not animate when paused or picking
             return false;
@@ -338,10 +347,7 @@ define([
 
         var animationOccured = false;
         var sceneTime = frameState.time;
-
         var model = this._model;
-        var scheduledAnimations = this._scheduledAnimations;
-        var length = scheduledAnimations.length;
 
         for (var i = 0; i < length; ++i) {
             var scheduledAnimation = scheduledAnimations[i];