Improve skinWasAltered performance

#15
TurboWarp/extensions#1153

Author: GarboMuffin

src/RenderWebGL.js

@@ -906,9 +906,10 @@ class RenderWebGL extends EventEmitter {
 
     skinWasAltered (skin) {
         // This is very hot function.
-        for (let i = 0; i < this._allDrawables.length; i++) {
-            const drawable = this._allDrawables[i];
-            if (drawable && drawable._skin === skin) {
+        for (let i = 0; i < this._drawList.length; i++) {
+            const drawableId = this._drawList[i];
+            const drawable = this._allDrawables[drawableId];
+            if (drawable._skin === skin) {
                 drawable._skinWasAltered();
             }
         }