Add 4.1 as stable version for PG

Playground/js/config_versions.js

@@ -10,6 +10,16 @@ CONFIG_last_versions = [
         "https://preview.babylonjs.com/loaders/babylonjs.loaders.min.js",
         "https://preview.babylonjs.com/serializers/babylonjs.serializers.min.js"
     ]],
+    ["4.1.0", [
+        "https://cdn.jsdelivr.net/gh/BabylonJS/Babylon.js@4.1.0/dist/babylon.js",
+        "https://cdn.jsdelivr.net/gh/BabylonJS/Babylon.js@4.1.0/dist/gui/babylon.gui.min.js",
+        "https://cdn.jsdelivr.net/gh/BabylonJS/Babylon.js@4.1.0/dist/inspector/babylon.inspector.bundle.js",
+        "https://cdn.jsdelivr.net/gh/BabylonJS/Babylon.js@4.1.0/dist/materialsLibrary/babylonjs.materials.min.js",
+        "https://cdn.jsdelivr.net/gh/BabylonJS/Babylon.js@4.1.0/dist/proceduralTexturesLibrary/babylonjs.proceduralTextures.min.js",
+        "https://cdn.jsdelivr.net/gh/BabylonJS/Babylon.js@4.1.0/dist/postProcessesLibrary/babylonjs.postProcess.min.js",
+        "https://cdn.jsdelivr.net/gh/BabylonJS/Babylon.js@4.1.0/dist/loaders/babylonjs.loaders.min.js",
+        "https://cdn.jsdelivr.net/gh/BabylonJS/Babylon.js@4.1.0/dist/serializers/babylonjs.serializers.min.js"
+    ]],
     ["4.0.3", [
         "https://cdn.jsdelivr.net/gh/BabylonJS/Babylon.js@4.0.3/dist/babylon.js",
         "https://cdn.jsdelivr.net/gh/BabylonJS/Babylon.js@4.0.3/dist/gui/babylon.gui.min.js",

Tools/DevLoader/BabylonLoader.js

@@ -120,7 +120,10 @@ var BABYLONDEVTOOLS;
         Loader.prototype.dequeue = function() {
             if (queue.length + esmQueue.length === 0) {
                 console.log('Scripts loaded');
-                BABYLON.Engine.ShadersRepository = "/src/Shaders/";
+
+                if (BABYLON) {
+                    BABYLON.Engine.ShadersRepository = "/src/Shaders/";
+                }
                 if (callback) {
                     callback();
                 }