ZStandard: Optimize passing the memory

In the case of decompression, we are using the same chunk of memory
twice. The first is to obtain the size of decompressed data, and
the second is to decompress it. In the current code, we are copying
the chunk of memory twice. The memory doesn't change between
the calls, so there is no point in copying it over and over.

Let's synchronize memory only during first call.

contrib/zstd/utils/utils_zstd.cc

@@ -80,7 +80,7 @@ absl::Status DecompressInMemory(ZstdApi& api, std::ifstream& in_stream,
 
   SAPI_ASSIGN_OR_RETURN(
       size_t desize, api.ZSTD_decompress(outbuf.PtrAfter(), size,
-                                         inbuf.PtrBefore(), inbuf.GetSize()));
+                                         inbuf.PtrNone(), inbuf.GetSize()));
   SAPI_ASSIGN_OR_RETURN(iserr, api.ZSTD_isError(desize));
   if (iserr) {
     return absl::UnavailableError("Unable to decompress file");