rtsp: Require the transport reply from the server to match the request

This fixes a crash if we requested TCP interleaved transport, but the
server replies with transport data for UDP. According to the RFC, the
server isn't allowed to respond with another transport type than the
one requested.

Originally committed as revision 26077 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/rtsp.c

@@ -1111,11 +1111,12 @@ static int make_setup_request(AVFormatContext *s, const char *host, int port,
             rt->transport = reply->transports[0].transport;
         }
 
-        /* close RTP connection if not chosen */
-        if (reply->transports[0].lower_transport != RTSP_LOWER_TRANSPORT_UDP &&
-            (lower_transport == RTSP_LOWER_TRANSPORT_UDP)) {
-            url_close(rtsp_st->rtp_handle);
-            rtsp_st->rtp_handle = NULL;
+        /* Fail if the server responded with another lower transport mode
+         * than what we requested. */
+        if (reply->transports[0].lower_transport != lower_transport) {
+            av_log(s, AV_LOG_ERROR, "Nonmatching transport in server reply\n");
+            err = AVERROR_INVALIDDATA;
+            goto fail;
         }
 
         switch(reply->transports[0].lower_transport) {