avcodec/mpeg4videodec: Fix integer overflow in mpeg4_decode_studio_block()

Fixes: signed integer overflow: 24023040 * 112 cannot be represented in type 'int'
Fixes: 16570/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_MPEG4_fuzzer-5173275211071488

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Reviewed-by: Kieran Kunhya <kierank@obe.tv>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/mpeg4videodec.c

@@ -1826,6 +1826,7 @@ static int mpeg4_decode_studio_block(MpegEncContext *s, int32_t block[64], int n
     uint32_t flc;
     const int min = -1 *  (1 << (s->avctx->bits_per_raw_sample + 6));
     const int max =      ((1 << (s->avctx->bits_per_raw_sample + 6)) - 1);
+    int shift =  3 - s->dct_precision;
 
     mismatch = 1;
 
@@ -1921,7 +1922,7 @@ static int mpeg4_decode_studio_block(MpegEncContext *s, int32_t block[64], int n
             else
                 block[j] = flc;
         }
-        block[j] = ((8 * 2 * block[j] * quant_matrix[j] * s->qscale) >> s->dct_precision) / 32;
+        block[j] = ((block[j] * quant_matrix[j] * s->qscale) * (1 << shift)) / 16;
         block[j] = av_clip(block[j], min, max);
         mismatch ^= block[j];
     }