[FIX] website_forum: avoid error when the sort param is encoded

Currently, when accessing a URL with a sorting encoded value,
the system will raise an error with a specific message, which
feels unfriendly to the user as well as saves unnecessary logs
in the log file. So we decoded that value, if except then sort
a page without sorting.

closes odoo/odoo#88847

X-original-commit: 82936a58
Signed-off-by: Romain Derie (rde) <rde@odoo.com>