[FIX] mrp_bom_cost: cost without BOM

- Activate variants
- On a product variant without BOM, go to Action > Compute Price from
  BOM

A zero-division is raised because of `... / bom.product_qty`.

opw-2067520

closes #36733

Signed-off-by: Nicolas Martinelli (nim) <nim@odoo.com>

addons/mrp_bom_cost/models/product.py

@@ -50,6 +50,8 @@ def _get_price_from_bom(self, boms_to_recompute=False):
 
     def _compute_bom_price(self, bom, boms_to_recompute=False):
         self.ensure_one()
+        if not bom:
+            return 0
         if not boms_to_recompute:
             boms_to_recompute = []
         total = 0