[FIX] stock_account: Preserve action_done return value

stock_account module override the action_done method of stock.move but does not return the same value
This causes problems when calling this function from xmlrpc because the resulting value is now None and that is not allowed to be marshaled by default.

addons/stock_account/stock_account.py

@@ -256,8 +256,9 @@ class stock_move(osv.osv):
 
     def action_done(self, cr, uid, ids, context=None):
         self.product_price_update_before_done(cr, uid, ids, context=context)
-        super(stock_move, self).action_done(cr, uid, ids, context=context)
+        res = super(stock_move, self).action_done(cr, uid, ids, context=context)
         self.product_price_update_after_done(cr, uid, ids, context=context)
+        return res
 
     def _store_average_cost_price(self, cr, uid, move, context=None):
         ''' move is a browe record '''