RTMP: fix FD leak in rtmp_open()

If we setup AVIO interrupt callback and it will be returns 1 on socket
timeouts and we try to connect to non-existing streams on some servers
(like nginx-rtmp) we got FD leak.

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/rtmpproto.c

@@ -2670,7 +2670,7 @@ reconnect:
         // audio or video packet arrives.
         while (!rt->has_audio && !rt->has_video && !rt->received_metadata) {
             if ((ret = get_packet(s, 0)) < 0)
-               return ret;
+               goto fail;
         }
 
         // Either after we have read the metadata or (if there is none) the