Double shipping rates: Default Package is always created even when a custom product package exists.

[tanmay3011]

Issue:
While using Fedex default package was always created even if when I had a customized a product_package for a product. So ended up getting double shipping rates.

Replication Steps:

1. Create a product_package with height, length, width, and weight. Keep default weight to be 0.
2. Now add that product(i.e.) to your order and move to the delivery step of order.

You will find double the expected shipping rate.

I could also find #81 issue. Any better solutions for it?