OSV-2020-1041 Use-of-uninitialized-value in McCopyWidthEq16_c

OSS-Fuzz report: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=13005 Crash type: Use-of-uninitialized-value Crash state: McCopyWidthEq16c WelsDec::BaseMC WelsDec::GetInterPred...