Simplify segfault fix
Simplify segfault fix

Take advantage of the fact that `chainLog <= windowLog`.

Cyan4973/zstd,Cyan4973/zstd,Majlen/zstd,ds77/zstd,Majlen/zstd,ds77/zstd,inikep/zstd,inikep/zstd,inikep/zstd,Cyan4973/zstd,inikep/zstd,ds77/zstd,Cyan4973/zstd,ds77/zstd,Cyan4973/zstd,Majlen/zstd,Majlen/zstd