avformat/4xm: Check for duplicate track ids

Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit dd949124)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/4xm.c

@@ -148,6 +148,9 @@ static int parse_strk(AVFormatContext *s,
         memset(&fourxm->tracks[fourxm->track_count], 0,
                sizeof(AudioTrack) * (track + 1 - fourxm->track_count));
         fourxm->track_count = track + 1;
+    } else {
+        if (fourxm->tracks[track].bits)
+            return AVERROR_INVALIDDATA;
     }
     fourxm->tracks[track].adpcm       = AV_RL32(buf + 12);
     fourxm->tracks[track].channels    = AV_RL32(buf + 36);