[19.0][FIX] sale_advance_payment: Add check for paid orders in portal

sale_advance_payment/models/sale.py

@@ -105,3 +105,10 @@ def _compute_advance_payment(self):
             order.payment_line_ids = mls
             order.amount_residual = amount_residual
             order.advance_payment_status = payment_state
+
+    def _has_to_be_paid(self):
+        # If an order 'has to be paid' it will show the "Accept & Pay" button in the
+        # portal. This prevents that, as you do't want customers payign for orders that
+        # are already paid
+        res = super()._has_to_be_paid()
+        return res and self.amount_residual > 0