avcodec/qdm2: Do not read out of array in fix_coding_method_array()

Instead we ask for a sample, its unclear what to do in this case.

Fixes: index 30 out of bounds for type 'int8_t [30][64]'
Fixes: 15339/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_QDM2_fuzzer-5749441484554240

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 ae021c1239)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/qdm2.c

@@ -406,7 +406,12 @@ static int fix_coding_method_array(int sb, int channels,
             }
             for (k = 0; k < run; k++) {
                 if (j + k < 128) {
-                    if (coding_method[ch][sb + (j + k) / 64][(j + k) % 64] > coding_method[ch][sb][j]) {
+                    int sbjk = sb + (j + k) / 64;
+                    if (sbjk > 29) {
+                        SAMPLES_NEEDED
+                        continue;
+                    }
+                    if (coding_method[ch][sbjk][(j + k) % 64] > coding_method[ch][sb][j]) {
                         if (k > 0) {
                             SAMPLES_NEEDED
                             //not debugged, almost never used