avcodec/iff: Check that video_size is large enough for the read parameters

video is allocated before parameters like bpp are read.

Fixes: out of array access
Fixes: 19084/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_IFF_ILBM_fuzzer-5718556033679360
Fixes: 19465/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_IFF_ILBM_fuzzer-5759908398235648

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpegSigned-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/iff.c

@@ -322,6 +322,8 @@ static int extract_header(AVCodecContext *const avctx,
             av_log(avctx, AV_LOG_ERROR, "Invalid number of bitplanes: %u\n", s->bpp);
             return AVERROR_INVALIDDATA;
         }
+        if (s->video_size && s->planesize * s->bpp * avctx->height > s->video_size)
+            return AVERROR_INVALIDDATA;
 
         av_freep(&s->ham_buf);
         av_freep(&s->ham_palbuf);