curl RTSP connection reuse routes response headers to the RTP callback (rtsp_conn state machine not reset between sessions)

libcurl's RTSP client keeps a per-connection RTP parsing state machine in `struct rtsp_conn` (`state`, `in_header`, `rtp_len`, `buf`). This state machine is initialised exactly once, when a brand-new connection is allocated, and is never reset thereafter. RTSP connections are pooled and reused …

// lib/rtsp.c:105-122  rtsp_setup_connection()
//   rtspc = Curl_conn_meta_get(...); curlx_calloc(...) -> all fields zero
//   (state = RTP_PARSE_SKIP, in_header = FALSE, rtp_len = 0, buf empty)
//   Called ONLY when a new connection is created — not on reuse.