BUG/MINOR: mux-quic: ignore STOP_SENDING for locally closed stream

BUG/MINOR: mux-quic: ignore STOP_SENDING for locally closed stream

It is possible to receive a STOP_SENDING frame for a locally closed
stream. This was not properly managed as this would result in a BUG_ON()
crash from qcs_idle_open() call under qcc_recv_stop_sending().

Now, STOP_SENDING frames are ignored when received on streams already
locally closed. This has two consequences depending on the reason of
closure :

* if a RESET_STREAM was already emitted and closed the stream, this
  patch prevents to emit a new RESET_STREAM. This behavior is thus
  better.

* if stream was closed due to all data transmitted, no RESET_STREAM will
  be built. This is contrary to the RFC 9000 which advice to transmit
  it, even on "Data Sent" state. However, this is not mandatory so the
  new behavior is acceptable, even if it could be improved.

This crash has been detected on haproxy.org. This can be artifically
reproduced by adding the following snippet at the end of qc_send_mux()
when doing a request with a small payload response :
  qcc_recv_stop_sending(qc->qcc, 0, 0);

This must be backported up to 2.6.