matroskadec: allow RealAudio/Cook/Sipro streams of flavor 0

Regression since 569d18aa.

Bug-Id: 1055
Cc: libav-stable@libav.org

libavformat/matroskadec.c

@@ -1916,7 +1916,7 @@ static int matroska_parse_tracks(AVFormatContext *s)
             track->audio.sub_packet_h    = avio_rb16(&b);
             track->audio.frame_size      = avio_rb16(&b);
             track->audio.sub_packet_size = avio_rb16(&b);
-            if (flavor                       <= 0 ||
+            if (flavor                        < 0 ||
                 track->audio.coded_framesize <= 0 ||
                 track->audio.sub_packet_h    <= 0 ||
                 track->audio.frame_size      <= 0 ||