[FIX] base: check grouping format
[FIX] base: check grouping format

If the user enters an incorrect grouping format, login won't be possible
anymore since the web client will crash when parsing the field value.

For example, "[3, 0,]" will trigger the issue.

Complement of commit 5959c41631ccc2d5eb1225f37f7002d7890fed13

opw-704388

bplancher/odoo,Elico-Corp/odoo_OCB,laslabs/odoo,Elico-Corp/odoo_OCB,bplancher/odoo,ygol/odoo,ygol/odoo,bplancher/odoo,hip-odoo/odoo,laslabs/odoo,ygol/odoo,hip-odoo/odoo,bplancher/odoo,ygol/odoo,ygol/odoo,bplancher/odoo,dfang/odoo,bplancher/odoo,hip-odoo/odoo,dfang/odoo,dfang/odoo,laslabs/odoo,Elico-Corp/odoo_OCB,laslabs/odoo,dfang/odoo,Elico-Corp/odoo_OCB,hip-odoo/odoo,hip-odoo/odoo,Elico-Corp/odoo_OCB,laslabs/odoo,dfang/odoo,Elico-Corp/odoo_OCB,dfang/odoo,ygol/odoo,laslabs/odoo,hip-odoo/odoo,ygol/odoo