OSV-2020-2068 Heap-buffer-overflow in WelsDec::Update8x8RefIdx

OSS-Fuzz report: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=26328 Crash type: Heap-buffer-overflow WRITE 1 Crash state: WelsDec::Update8x8RefIdx WelsDec::ParseInterBMotionInfoCabac WelsDec::WelsDecodeMbCabacBSliceBaseMode0...