set FSocketInitialized to False in TSocketStream.Close (fix AV when Close is called twice)

packages/fcl-net/src/ssockets.pp

@@ -717,6 +717,7 @@ begin
   DoOnClose;
   if FSocketInitialized then
     FHandler.Close; // Ignore the result
+  FSocketInitialized:=False;
   FreeAndNil(FHandler);
   CloseSocket(Handle);
   FClosed:=True;