Fix input size too small to trigger zstdmt
Fix input size too small to trigger zstdmt

Majlen/zstd,Cyan4973/zstd,Majlen/zstd,Cyan4973/zstd,Cyan4973/zstd,Cyan4973/zstd,Cyan4973/zstd,Majlen/zstd,Majlen/zstd