avcodec/smc: Check input packet size

Fixes: Timeout
Fixes: 6261/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_SMC_fuzzer-5811309653262336

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpegSigned-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit 02936634)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/smc.c

@@ -437,6 +437,10 @@ static int smc_decode_frame(AVCodecContext *avctx,
     SmcContext *s = avctx->priv_data;
     const uint8_t *pal = av_packet_get_side_data(avpkt, AV_PKT_DATA_PALETTE, NULL);
     int ret;
+    int total_blocks = ((s->avctx->width + 3) / 4) * ((s->avctx->height + 3) / 4);
+
+    if (total_blocks / 1024 > avpkt->size)
+        return AVERROR_INVALIDDATA;
 
     bytestream2_init(&s->gb, buf, buf_size);