Improve decoder to recognise child object

[OGKevin]

Steps to reproduce:

1. Try and decode a child object into a model that is expecting its parent

What should happen:

1. The model is correctly populated with data.

What happens:

1. All the fields, including the parent field will be null.

Logs

• Logs no logs

Extra info:

• Tested on 0.12.2

Reference

• Improve decoder to recognise child objects  sdk_php#68