[13.0][IMP] account_invoicing_mode_at_shipping

With a picking related to multiple sales order and those sales order
with different invoicing mode, the invoicing could happen at the wrong
moment or not at all.

This change unifies the way the module checks for sales order needed to
be invoiced at shipping.

account_invoice_mode_at_shipping/models/stock_picking.py

@@ -17,12 +17,18 @@ def action_done(self):
                 picking.with_delay()._invoicing_at_shipping()
         return res
 
+    def _get_sales_order_to_invoice_at_shipping(self):
+        """Returns sales order to invoice at shipping related to the picking."""
+        return self.mapped("move_lines.sale_line_id.order_id").filtered(
+            lambda r: r.partner_invoice_id.invoicing_mode == "at_shipping"
+        )
+
     def _invoice_at_shipping(self):
         """Check if picking must be invoiced at shipping."""
         self.ensure_one()
         return (
             self.picking_type_code == "outgoing"
-            and self.sale_id.partner_invoice_id.invoicing_mode == "at_shipping"
+            and self._get_sales_order_to_invoice_at_shipping()
         )
 
     @job(default_channel="root.invoice_at_shipping")
@@ -44,6 +50,5 @@ def _invoicing_at_shipping(self):
         return invoices or _("Nothing to invoice.")
 
     def _get_sales_order_to_invoice(self):
-        return self.mapped("move_lines.sale_line_id.order_id").filtered(
-            lambda r: r._get_invoiceable_lines()
-        )
+        sales = self._get_sales_order_to_invoice_at_shipping()
+        return sales.filtered(lambda r: r._get_invoiceable_lines())