[FIX] stock_landed_costs: prevent crash

Prevent crash if `stock_valuation_layer_ids` is an empty recordset. Note
that the original issue is solved with #43017, but requires an upgrade
of the module.

opw-2172049

closes odoo/odoo#43289

X-original-commit: 8a1ce12aee326b59f33f48804a4cfca61dab7506
Signed-off-by: Nicolas Martinelli (nim) <nim@odoo.com>

addons/stock_landed_costs/models/stock_landed_cost.py

@@ -122,7 +122,7 @@ class LandedCost(models.Model):
             }
             for line in cost.valuation_adjustment_lines.filtered(lambda line: line.move_id):
                 remaining_qty = sum(line.move_id.stock_valuation_layer_ids.mapped('remaining_qty'))
-                linked_layer = line.move_id.stock_valuation_layer_ids[0]
+                linked_layer = line.move_id.stock_valuation_layer_ids[:1]
 
                 # Prorate the value at what's still in stock
                 cost_to_add = (remaining_qty / line.move_id.product_qty) * line.additional_landed_cost