Fixed hang in SslStreamBase when stream is closed during I/O

Fixed hang in SslStreamBase when stream is closed during I/O

If the SslStreamBase is disposed while a read or write operation is in progress, the asynchronous I/O state is never marked as completed, resulting in synchronous Read/Write calls never returning. To fix this, the internal I/O callbacks should mark the asynchronous operations as completed, possibly with an error, even if the SslStreamBase is disposed.