zstreamtest : add test which detects when ZSTD_initCStream() inflate data
zstreamtest : add test which detects when ZSTD_initCStream() inflate data

as in #942, when ZSTD_initCStream() believes data is empty, instead of unknown.

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