OSV-2020-2078 Heap-buffer-overflow in WelsDec::UpdateP16x16RefIdx

OSS-Fuzz report: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=26389 Crash type: Heap-buffer-overflow WRITE 2 Crash state: WelsDec::UpdateP16x16RefIdx WelsDec::PredBDirectTemporal WelsDec::ParseInterBInfo...