[FIX] product: set disp. name to New if creating

**Current behavior:**
When creating a new product template record, the tab title will
be *Odoo - False* until a new name is saved rather than
*Odoo - New*.

**Expected behavior:**
When creating a new record in a form view, the tab title will be
*Odoo - New* until the `name` field is filled out and the record
gets saved (at which point it will be *Odoo - <name>*).

**Steps to reproduce:**
1. Install `sale_management` and go to the product list view

2. Create a new product, observe the misnamed tab title

**Cause of the issue:**
In `product.template`'s _compute_display_name() method, some of
the default values can have a 'False' (str) value which will
evaluate to True (bool), setting the name to 'False'.

**Fix:**
Set the display_name field to a False (bool) value if the
current record does not have a name field set.

opw-3793588

closes odoo/odoo#157258

Signed-off-by: Morgane Demesmaeker <edm@odoo.com>

addons/product/models/product_template.py

@@ -519,7 +519,10 @@ class ProductTemplate(models.Model):
     @api.depends('name', 'default_code')
     def _compute_display_name(self):
         for template in self:
-            template.display_name = '{}{}'.format(template.default_code and '[%s] ' % template.default_code or '', template.name)
+            template.display_name = False if not template.name else (
+                '{}{}'.format(
+                    template.default_code and '[%s] ' % template.default_code or '', template.name
+                ))
 
     @api.model
     def _name_search(self, name, domain=None, operator='ilike', limit=None, order=None):