Impacted versions: 9.0

Steps to reproduce:

* Create an MTO product with 
  * Product Type: Stockable Product
  * Routes: "Buy" and "Make to Order"
* Update Qty on Hand to any quantity (i.e, 2).
* Create a sales order with this product and a number <= to the one in the step before.
* Confirm the sales order.

Current behavior:

The created delivery picking appears in state "Reserved" and the current quantity on stock has been reserved, allowing you to transfer that stock.

Expected behavior:

The created delivery picking should be in "Waiting another operation", or at least in "Waiting availability" until the purchase order is confirmed (if you have defined a supplier for the product and the procurement creates the purchase order), which seems to be the current behavior when there's no stock available (is this also correct, as it allows to manually reserve?).
res = {}
        for inv in self.browse(cr, uid, ids, context=context):
            res[inv.id] = False
            if inv.move_ids:
                res[inv.id] = True
        return res
    def _get_available_filters(self, cr, uid, context=None):
        """
           This function will return the list of filter allowed according to the options checked
           in 'Settings\Warehouse'.
           :rtype: list of tuple
        """
        
        res_filter = [('none', _('All products')), ('partial', _('Select products manually')), ('product', _('One product only'))]
        if self.pool.get('res.users').has_group(cr, uid, 'stock.group_tracking_owner'):
            res_filter.append(('owner', _('One owner only')))
            res_filter.append(('product_owner', _('One product for a specific owner')))
        if self.pool.get('res.users').has_group(cr, uid, 'stock.group_production_lot'):
            res_filter.append(('lot', _('One Lot/Serial Number')))
        if self.pool.get('res.users').has_group(cr, uid, 'stock.group_tracking_lot'):
            res_filter.append(('pack', _('A Pack')))
        return res_filter
    def _get_total_qty(self, cr, uid, ids, field_name, args, context=None):