We only care about non-cart orders and skipping carts, saves PostgreSQL
query planner to go through thousands of records in production use cases
(my food hub).
We go from
```sql
-> Index Scan using index_spree_orders_on_customer_id on spree_orders (cost=0.42..12049.45 rows=152002 width=15) (actual time=0.015..11.703 rows=13867 loops=1)
```
to
```sql
-> Index Scan using index_spree_orders_on_customer_id on spree_orders (cost=0.42..12429.46 rows=10802 width=15) (actual time=0.025..17.705 rows=9954 loops=1)
```