[FIX] product: don't remove product_tmpl_id from supplierinfo

Versions
--------
- 15.0+

Steps
-----
1. Go to product variants;
2. select a product;
3. add a new Vendor line in the Purchase tab;
4. save;
5. add another Vendor line;
6. save.

Issue
-----
Previous line disappears from view.

Cause
-----
In 93bc96047ff684cb66b69186822493815cf37982 I added logic which sets
the `product_tmpl_id` in `product.supplierinfo` if a `product_id`
gets written without accompanying `product_tmpl_id`. Adding lines from
the Product Variant views add  `{'product_id': False}` to the values for
every vendor in the list without a Product Variant, so their
`product_tmpl_id` gets overwritten with the `product_tmpl_id` of an
empty product.

Solution
--------
Only overwrite `product_tmpl_id` iff `product_id` gets written to a
non-falsy value by changing `if 'product_id' in vals` to
`if vals.get('product_id')`.

opw-3664524

closes odoo/odoo#153168

X-original-commit: 03d4be7b8804863a7e7e9af29a8ec61c65d6dab3
Signed-off-by: Quentin Wolfs (quwo) <quwo@odoo.com>
Signed-off-by: Levi Siuzdak <sile@odoo.com>

addons/product/models/product_supplierinfo.py

@@ -86,7 +86,8 @@ class SupplierInfo(models.Model):
 
     def _sanitize_vals(self, vals):
         """Sanitize vals to sync product variant & template on read/write."""
-        if 'product_id' in vals and 'product_tmpl_id' not in vals:
+        # add product's product_tmpl_id if none present in vals
+        if  vals.get('product_id') and not vals.get('product_tmpl_id'):
             product = self.env['product.product'].browse(vals['product_id'])
             vals['product_tmpl_id'] = product.product_tmpl_id.id
 

addons/product/tests/test_seller.py

@@ -146,3 +146,6 @@ class TestSeller(TransactionCase):
         }])
         self.assertEqual(vendors, self.product_consu.seller_ids,
             "Sellers of a product should be listed in the product's seller_ids")
+        vendors.write({'product_id': False})
+        self.assertEqual(vendors, self.product_consu.seller_ids,
+            "Setting the product_id to False shouldn't affect seller_ids.")