[FIX] orm: Fix a bug in _read_group_fill_temporal.
[FIX] orm: Fix a bug in _read_group_fill_temporal.

_read_group_fill_temporal was returning a None value instand of a [] when its
'data' parameter was an empty array, resulting in crash in graph_view.

ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo