OSV-2020-2076 Use-of-uninitialized-value in UpdateDecStatNoFreezingInfo

OSS-Fuzz report: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=26346 Crash type: Use-of-uninitialized-value Crash state: UpdateDecStatNoFreezingInfo UpdateDecStat WelsDec::DecodeFrameConstruction...