OSV-2020-2077 UNKNOWN READ in WelsCommon::WelsFree

OSS-Fuzz report: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=26347 Crash type: UNKNOWN READ Crash state: WelsCommon::WelsFree WelsCommon::CMemoryAlign::WelsFree WelsDec::FreePicture...