Minor bug fixed: unreadCount property was not correctly updated

It is not the best solution but I think it solves a problem about updating correctly the unreadCount property. Messages have being set to unread = NO, and later when the success block is executed to update the unreadCount, message is already defined as unread=NO and the code doesn't execute unreadCount property decrement. Please, check this before because I'm not seeing all the scope of the context.