Bug#944223: Acknowledgement (lz4 SIGSEGV in LZ4_decompress_generic)

[Mihail Safronov]

Problem is more complex. When receive incomplete stream, decompression
context need to be reset with LZ4F_resetDecompressionContext (added in
lz4 1.8.0).

I add simple port (this is for lz4 1.7 in CentOS 7)

void LZ4F_resetDecompressionContext(LZ4F_dctx* dctx)
{
    dctx->dStage = dstage_getHeader;
    dctx->dict = NULL;
    dctx->dictSize = 0;
}

And with first patch problem was solved.