[FIX] stock_landed_costs: avoid useless multiple writes

Initialise quant_dict inside for loop as doing outside loops
renders to be a quadratic write of quant object due to the fact that
previous quants are kept each time a new valuation line is read.
In case of posting a Landed Cost record with a huge amount of cost_lines
and huge amount of stock_move having several quants would result in a
extra overhead.

Closes #9005

addons/stock_landed_costs/stock_landed_costs.py

@@ -202,13 +202,13 @@ class stock_landed_cost(osv.osv):
             if not cost.valuation_adjustment_lines or not self._check_sum(cr, uid, cost, context=context):
                 raise osv.except_osv(_('Error!'), _('You cannot validate a landed cost which has no valid valuation lines.'))
             move_id = self._create_account_move(cr, uid, cost, context=context)
-            quant_dict = {}
             for line in cost.valuation_adjustment_lines:
                 if not line.move_id:
                     continue
                 per_unit = line.final_cost / line.quantity
                 diff = per_unit - line.former_cost_per_unit
                 quants = [quant for quant in line.move_id.quant_ids]
+                quant_dict = {}
                 for quant in quants:
                     if quant.id not in quant_dict:
                         quant_dict[quant.id] = quant.cost + diff