OSV-2021-916 Use-of-uninitialized-value in jxl::ModularFrameDecoder::DecodeAcMetadata

OSS-Fuzz report: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=35778 Crash type: Use-of-uninitialized-value Crash state: jxl::ModularFrameDecoder::DecodeAcMetadata jxl::FrameDecoder::ProcessDCGroup jxl::ThreadPool::RunCallStatejxl::Status...