fix: SynBidirSock.pas raise access violation errors when ProcessMask()

[ysair]

1. run Project31WinHTTPEchoServer.exe
2. execute this test code:

   var
   Client :  THttpClientWebSockets;
   protocol : TWebSocketProtocol;
   frame: TWebSocketFrame;
   begin
   protocol := TWebSocketProtocolChat.Create('meow', 'whatever');
   Client := THttpClientWebSockets.WebSocketsConnect(
     'localhost','8888',protocol, nil, '', 'whatever');
   frame.opcode  :=  focText;
   frame.content :=  [];
   frame.payload :=  'test1234';
   Client.WebSockets.SendFrame(frame); //av error
   Client.free;
   end;

[synopse]

I have made two commits to fix the RemoteIP issue and properly document TWebSocketFrame.payload use.