[IMP] pos_mercury: prevent multiple electronic payments
[IMP] pos_mercury: prevent multiple electronic payments

If there is a Vantiv payment line, adding terminal payment line (e.g.
Adyen) was possible because Vantiv payment line is not recognized as
electronic payment. This commit generalizes the behavior where new
paymentline is prevented if there is a pending electronic payment.

task-id: 1984690
ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo