avdemux: tell avformat that input is stream

Thisways find_stream_info() doesn't get stuck with some http-streams (like
http://bglive-a.bitgravity.com/twit/live/high ) when trying to seek. Fix #3080

modules/demux/avformat/demux.c

@@ -199,6 +199,13 @@ int OpenDemux( vlc_object_t *p_this )
     p_sys->url.prot->next = 0;
     init_put_byte( &p_sys->io, p_sys->io_buffer, p_sys->io_buffer_size,
                    0, &p_sys->url, IORead, NULL, IOSeek );
+    /* Tell avformat that input is stream, so it doesn't get stuck
+       when trying av_find_stream_info() trying to seek all the wrong places
+       init_put_byte defaults io.is_streamed=0, so thats why we set them after it
+       */
+    p_sys->url.is_streamed = 1;
+    p_sys->io.is_streamed = 1;
+
 
     /* Open it */
     if( av_open_input_stream( &p_sys->ic, &p_sys->io, p_demux->psz_path,