avformat/iamf_parse: Check sound_system

Fixes: index 13 out of bounds for type 'const struct IAMFSoundSystemMap [13]'
Fixes: 67796/clusterfuzz-testcase-minimized-ffmpeg_dem_IAMF_fuzzer-4554553191104512

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit 4593cf7ab3)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/iamf_parse.c

@@ -933,6 +933,10 @@ static int mix_presentation_obu(void *s, IAMFContext *c, AVIOContext *pb, int le
             if (submix_layout->layout_type == 2) {
                 int sound_system;
                 sound_system = (byte >> 2) & 0xF;
+                if (sound_system >= FF_ARRAY_ELEMS(ff_iamf_sound_system_map)) {
+                    ret = AVERROR_INVALIDDATA;
+                    goto fail;
+                }
                 av_channel_layout_copy(&submix_layout->sound_system, &ff_iamf_sound_system_map[sound_system].layout);
             }