avformat/iamf_parse: 0 layers are not allowed

Fixes: out of array access
Fixes: 68302/clusterfuzz-testcase-minimized-ffmpeg_DEMUXER_fuzzer-4665793796177920

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Reviewed-by: James Almer <jamrial@gmail.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/iamf_parse.c

@@ -330,7 +330,7 @@ static int scalable_channel_layout_config(void *s, AVIOContext *pb,
     nb_layers = avio_r8(pb) >> 5; // get_bits(&gb, 3);
     // skip_bits(&gb, 5); //reserved
 
-    if (nb_layers > 6)
+    if (nb_layers > 6 || nb_layers == 0)
         return AVERROR_INVALIDDATA;
 
     audio_element->layers = av_calloc(nb_layers, sizeof(*audio_element->layers));