[FIX] calendar: prevent traceback if no real_ids After 488e9f2 there is traceback if the list real_ids is empty.
[FIX] calendar: prevent traceback if no real_ids
After 488e9f2 there is traceback
if the list real_ids is empty.

opw-690761

hip-odoo/odoo,dfang/odoo,ygol/odoo,ygol/odoo,dfang/odoo,dfang/odoo,hip-odoo/odoo,hip-odoo/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,hip-odoo/odoo,dfang/odoo,dfang/odoo,dfang/odoo,hip-odoo/odoo,hip-odoo/odoo