Fix mat id issue

dist/preview release/babylon.max.js

@@ -24570,7 +24570,7 @@ var BABYLON;
             this._wasPreviouslyReady = false;
             this._fillMode = Material.TriangleFillMode;
             this.name = name;
-            this.id = name;
+            this.id = name || BABYLON.Tools.RandomId();
             this._scene = scene || BABYLON.Engine.LastCreatedScene;
             if (this._scene.useRightHandedSystem) {
                 this.sideOrientation = Material.ClockWiseSideOrientation;

src/Materials/babylon.material.ts

@@ -349,7 +349,7 @@
 
         constructor(name: string, scene: Scene, doNotAdd?: boolean) {
             this.name = name;
-            this.id = name;
+            this.id = name || Tools.RandomId();
 
             this._scene = scene || Engine.LastCreatedScene;