[FTP/FTPS Only] Completes the asynchronous operation started in BeginGetFeatures.
string-array containing server features, or null if no features or not supported.
Before calling BeginGetFeatures, you need to create a callback method that implements the AsyncCallback delegate. This callback method executes in a separate thread and is called by the system after BeginGetFeatures returns. The callback method must accept the IAsyncResult returned by the BeginGetFeatures method as a parameter. This parameter may then be passed to the EndGetFeatures method to complete the operation.