Avoid duplicate loads on creating item adjustments

This reduces a source of duplicate records loads that can lead do deadlocks and identity problems.

We oversaw this one on the deduploads optimization branch.

After merging I'm gonna squash this commit into the deduploads one on the next rebase.
I know this is outside the changes, but if `:order` is always expected this should probably be:

```ruby
order = payload.fetch(:order)
```