Tells TElSSLServer that there are data in the socket to be taken.
Use this method to tell TElSSLServer that there are data in the socket. TElSSLServer then fires
OnReceive event to read the block of data.
If the application uses one of wait methods to check availability of the data in the socket (select() or WaitFor* API functions), the place to call DataAvailable is right after the call to those wait methods.