eio,lwt,mirage: fix drain_handshake on Read_closed/Write_closed states drain_handshake only returned early for `Active tls` when the handshake was no longer in progress. `Read_closed` and `Write_closed` fell through to the `| _ ->` branch, which called read_react — raising End_of_file even though the handshake had completed successfully. This can happen when the peer's Finished and close_notify arrive in the same read batch, causing handle_tls to transition the state to `Read_closed` before drain_handshake can check handshake_in_progress.