[FIX] product: report pricelist empty data

Try to get the report_pricelist with empty data
(Studio Report editor can)

Before this commit, it crashes because we tried to access dict keys directly
in an empty dict

After this commit, it doesn't crash

OPW 2009862

closes odoo/odoo#34118

Signed-off-by: Lucas Perais (lpe) <lpe@odoo.com>