avcodec/hcadec: do not allow code to continue after failed init

Fixes: 62285/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_HCA_fuzzer-6247136417087488
Fixes: out of array write

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 48eeb198a5)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/hcadec.c

@@ -538,8 +538,10 @@ static int decode_frame(AVCodecContext *avctx, AVFrame *frame,
             return AVERROR_INVALIDDATA;
         } else if (AV_RB16(avpkt->data + 6) <= avpkt->size) {
             ret = init_hca(avctx, avpkt->data, AV_RB16(avpkt->data + 6));
-            if (ret < 0)
+            if (ret < 0) {
+                c->crc_table = NULL; // signal that init has not finished
                 return ret;
+            }
             offset = AV_RB16(avpkt->data + 6);
             if (offset == avpkt->size)
                 return avpkt->size;