[FIX] website_sale: add missing method check

Backport of https://github.com/odoo/odoo/commit/c88f76cab7a1292e6fff3bd77441a9845b8173c8

 because it could lead to a traceback in the case a GET wasn't supposed to receive this kind of format as request answer.

closes odoo/odoo#100674

Signed-off-by: Yannick Tivisse (yti) <yti@odoo.com>