[FIX] delivery: avoid a traceback when calculating the shipping cost

Stpes to reproduce the bug:
- Install delivery_ups
- Go to shipping method > UPS BE > Package type
- Set the max weight to 10 kg
- Create a product “P1”:
    - Go to inventory tab > weight: 10 kg
- Create a SO:
    - Add the product “P1”
    - Add shipping
    - Select UPS Be
    - Click on get rate

 Problem:
Traceback is triggered, because we devise a number by an empty list:
https://github.com/odoo/odoo/blob/6b0ab28791f4a29254d294f8a116545d4c124e8b/addons/delivery/models/delivery_carrier.py#L301

The `last_package_weight` is the result of the modulo of the weight of
all the products by the maximum weight of a package, in this case it is:
0 -> 10% 10

We then use this result to calculate the weight of the package,
but parenthesis have been forgotten and therefore an empty list is
returned in the case where `last_package_weight` is 0

https://github.com/odoo/odoo/blob/6b0ab28791f4a29254d294f8a116545d4c124e8b/addons/delivery/models/delivery_carrier.py#L298-L300



opw-3075295

closes odoo/odoo#106780

Signed-off-by: William Henrotin (whe) <whe@odoo.com>