[FIX] product: Add products without 'combination_indices' to cart.

Sometimes when we try to buy a product that doesn't have any variants,
it would result in an error saying there isn't any valid combination
for that product.

This was happening because `_get_variant_id_for_combination` was
considering that the field `combination_indices` would always be
equal to `''` (empty string) in such a case.

This isn't true as `combination_indices` isn't a required field
thus allowing `null` \ `None` to be valid values for that field.

This fix will simply include products with no values set for their
`combination_indices` when searching a corresponding variant from
the `product_template`.

closes odoo/odoo#44056

X-original-commit: 03e7efc3b4592c5f063c665130011a91fcc4d683
Signed-off-by: Toufik Benjaa (tbe) <tbe@odoo.com>

0 files changed, 0 insertions, 0 deletions