[FIX] wrong sql calculation on credit and debit value

https://github.com/OCA/account-financial-reporting/issues/443

customer_outstanding_statement/report/customer_outstanding_statement.py

@@ -52,12 +52,12 @@ class CustomerOutstandingStatement(models.AbstractModel):
             SELECT m.name as move_id, l.partner_id, l.date, l.name,
                             l.ref, l.blocked, l.currency_id, l.company_id,
             CASE WHEN (l.currency_id is not null AND l.amount_currency > 0.0)
-                THEN sum(l.amount_currency)
-                ELSE sum(l.debit)
+                THEN avg(l.amount_currency)
+                ELSE avg(l.debit)
             END as debit,
             CASE WHEN (l.currency_id is not null AND l.amount_currency < 0.0)
-                THEN sum(l.amount_currency * (-1))
-                ELSE sum(l.credit)
+                THEN avg(l.amount_currency * (-1))
+                ELSE avg(l.credit)
             END as credit,
             CASE WHEN l.balance > 0.0
                 THEN l.balance - sum(coalesce(pd.amount, 0.0))