avcodec/fic: Fail on invalid slice size/off

Fixes: Timeout
Fixes: 11486/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_FIC_fuzzer-5677133863583744

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 30a7a81cdc)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/fic.c

@@ -380,6 +380,8 @@ static int fic_decode_frame(AVCodecContext *avctx, void *data,
             slice_h      = FFALIGN(avctx->height - ctx->slice_h * (nslices - 1), 16);
         } else {
             slice_size = AV_RB32(src + tsize + FIC_HEADER_SIZE + slice * 4 + 4);
+            if (slice_size < slice_off)
+                return AVERROR_INVALIDDATA;
         }
 
         if (slice_size < slice_off || slice_size > msize)