[FIX] sale_stock: payment_term in supplier invoice

When invoicing a supplier, this is the supplier payment term which
has to be taken into account.

opw:656307

addons/sale_stock/sale_stock.py

@@ -480,7 +480,7 @@ class stock_picking(osv.osv):
     def _get_invoice_vals(self, cr, uid, key, inv_type, journal_id, move, context=None):
         inv_vals = super(stock_picking, self)._get_invoice_vals(cr, uid, key, inv_type, journal_id, move, context=context)
         sale = move.picking_id.sale_id
-        if sale:
+        if sale and inv_type in ('out_invoice', 'out_refund'):
             inv_vals.update({
                 'fiscal_position': sale.fiscal_position.id,
                 'payment_term': sale.payment_term.id,