Added Accessor initializers

Added Accessor intializers
Now byteOffset and normalized are initialized to their default
values. componentType and Type are initialized to bad values
on purpose, they must be set when loading or creating the model.

tiny_gltf.h

@@ -887,8 +887,13 @@ struct Accessor {
     // unreachable return 0;
   }
 
-  Accessor() {
-    bufferView = -1;
+  Accessor() :
+    bufferView(-1),
+    byteOffset(0),
+    normalized(false),
+    componentType(-1),
+    count(0),
+    type(-1){
     sparse.isSparse = false;
   }
   DEFAULT_METHODS(Accessor)