OSV-2021-245 UNKNOWN WRITE in WelsDecodeBs

OSS-Fuzz report: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=29969 Crash type: UNKNOWN WRITE Crash state: WelsDecodeBs WelsDec::CWelsDecoder::DecodeFrame2WithCtx WelsDec::CWelsDecoder::DecodeFrame2...