Improve code style of Shopware_Components_Document->values4x()

We had a hard time figuring out what the `netto` config flag really does in every possible case, so we wanted to document our findings. While we where at it, we also made the code, specifically the first `array_merge()`, more readable by improving the code style.

This PR is based on current master and does not introduce any logical changes, it's purely cosmetic.