Objects instanced in c++ can't be bound to typed gdscript variables

GDNative:
```c++
class MyCustomType : public godot::Node
{
GODOT_CLASS(MyCustomType, godot::Node);
public:
void calling();
void functions();
void works();
void fine();
};

// ...

class Manager: public godot::Node
{
GODOT_CLASS(Manager, godot::Node);
public:
MyCustomType* make_custom_object()
{
auto object = MyCustomType::_new();
add_child(object);
return object;
}
};
```

The .gdns file:
```
[gd_resource type="NativeScript" load_steps=2 format=2]

[ext_resource path="res://bin/test.gdnlib" type="GDNativeLibrary" id=1]

[resource]
class_name = "MyCustomType"
library = ExtResource( 1 )
script_class_name = "MyCustomType"
```

GDScript:
```gdscript
var o = Manager.make_custom_object()

o.calling()
o.functions()
o.works()
o.fine()

var test:MyCustomType = o #error
```

Also, if the variable is a function parameter, e.g.:
```gdscript
func broken(param:MyCustomType):
pass

# ...

var o = Manager.make_custom_object()

broken(o)
```
...then no runtime error is produced, but param will be `null`