avformat/iamf_parse: reject ambisonics mode > 1

ambisonics mode > 1 does not initialize any layer but layer 0
is unconditionally dereferenced

Fixes: poc-2024-11
Fixes: null pointer dereference
Found-by: 苏童 <220235212@seu.edu.cn>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/iamf_parse.c

@@ -413,7 +413,7 @@ static int ambisonics_config(void *s, AVIOContext *pb,
 
     ambisonics_mode = ffio_read_leb(pb);
     if (ambisonics_mode > 1)
-        return 0;
+        return AVERROR_INVALIDDATA;
 
     output_channel_count = avio_r8(pb);  // C
     substream_count = avio_r8(pb);  // N