Fixes: Timeout & OOM
Fixes: 28701/clusterfuzz-testcase-minimized-ffmpeg_dem_IFF_fuzzer-5185094964871168
Fixes: 29116/clusterfuzz-testcase-minimized-ffmpeg_dem_IFF_fuzzer-4874284795297792

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