Fix PBR clone functions

src/Materials/PBR/babylon.pbrMaterial.ts

@@ -648,7 +648,12 @@
         }         
 
         public clone(name: string): PBRMaterial {
-            return SerializationHelper.Clone(() => new PBRMaterial(name, this.getScene()), this);
+            var clone = SerializationHelper.Clone(() => new PBRMaterial(name, this.getScene()), this);
+
+            clone.id = name;
+            clone.name = name;
+
+            return clone;
         }
 
         public serialize(): any {

src/Materials/PBR/babylon.pbrMetallicRoughnessMaterial.ts

@@ -103,7 +103,12 @@
         }        
 
         public clone(name: string): PBRMetallicRoughnessMaterial {
-            return SerializationHelper.Clone(() => new PBRMetallicRoughnessMaterial(name, this.getScene()), this);
+            var clone = SerializationHelper.Clone(() => new PBRMetallicRoughnessMaterial(name, this.getScene()), this);
+            
+            clone.id = name;
+            clone.name = name;
+
+            return clone;
         }
 
         /**

src/Materials/PBR/babylon.pbrSpecularGlossinessMaterial.ts

@@ -95,7 +95,12 @@
         }
 
         public clone(name: string): PBRSpecularGlossinessMaterial {
-            return SerializationHelper.Clone(() => new PBRSpecularGlossinessMaterial(name, this.getScene()), this);
+            var clone = SerializationHelper.Clone(() => new PBRSpecularGlossinessMaterial(name, this.getScene()), this);
+
+            clone.id = name;
+            clone.name = name;
+
+            return clone;            
         }
 
         /**