[FIX] mrp: correct workorder qty_producing onchange

When changing the quantity being produced on a work order and
serial numbers are consumed, we need to delete or add lines
for every serial number in function of the quantity through the onchange.

We changed the quantity_done to be set to quantity by default (automatically)
as otherwise we forgot to set it.  But for the onchange, it means
we need to take it into account otherwise the number of records
would not be diminished.

addons/mrp/models/mrp_workorder.py

@@ -213,11 +213,15 @@ class MrpWorkorder(models.Model):
                     for move_lot in move_lots:
                         if qty_todo <= 0:
                             break
-                        if move_lot.quantity_done == 0 and qty_todo > move_lot.quantity:
+                        if not move_lot.lot_id and qty_todo >= move_lot.quantity:
                             qty_todo = qty_todo - move_lot.quantity
                             self.active_move_lot_ids -= move_lot  # Difference operator
                         else:
                             move_lot.quantity = move_lot.quantity - qty_todo
+                            if move_lot.quantity_done - qty_todo > 0:
+                                move_lot.quantity_done = move_lot.quantity_done - qty_todo
+                            else:
+                                move_lot.quantity_done = 0
                             qty_todo = 0
 
     @api.multi