Update to 7-Zip 17.01 Beta from Igor Pavlov

- Minor speed optimization for LZMA2 (xz and 7z) multi-threading compression.
  7-Zip now uses additional memory buffers for multi-block LZMA2 compression.
  CPU utilization was slightly improved.
- 7-zip now creates multi-block xz archives by default. Block size can be
  specified with -ms[Size]{m|g} switch.
- xz decoder now can unpack random block from multi-block xz archives.  7-Zip
  File Manager now can open nested multi-block xz archives (for example,
  image.iso.xz) without full unpacking of xz archive.
- 7-Zip now can create zip archives from stdin to stdout.
- 7-Zip command line: @listfile now doesn't work after -- switch.  Use
  -i@listfile before -- switch instead.

fixed bugs:
- 7-Zip could add unrequired alternate file streams to WIM archives, for
  commands that contain filename wildcards and -sns switch.
- 7-Zip 17.00 beta crashed for commands that write anti-item to 7z archive.
- 7-Zip 17.00 beta ignored "Use large memory pages" option.

CPP/7zip/UI/Agent/Agent.cpp

@@ -1453,7 +1453,12 @@ STDMETHODIMP CAgentFolder::Extract(const UInt32 *indices,
     pathMode = NExtract::NPathMode::kNoPathnames;
   */
 
-  extractCallbackSpec->InitForMulti(false, pathMode, overwriteMode);
+  extractCallbackSpec->InitForMulti(
+      false, // multiArchives
+      pathMode,
+      overwriteMode,
+      true  // keepEmptyDirPrefixes
+      );
 
   if (extractCallback2)
     extractCallback2->SetTotal(_agentSpec->GetArc().GetEstmatedPhySize());
@@ -1717,7 +1722,12 @@ STDMETHODIMP CAgent::Extract(
   COM_TRY_BEGIN
   CArchiveExtractCallback *extractCallbackSpec = new CArchiveExtractCallback;
   CMyComPtr<IArchiveExtractCallback> extractCallback = extractCallbackSpec;
-  extractCallbackSpec->InitForMulti(false, pathMode, overwriteMode);
+  extractCallbackSpec->InitForMulti(
+      false, // multiArchives
+      pathMode,
+      overwriteMode,
+      true  // keepEmptyDirPrefixes
+      );
 
   CExtractNtOptions extractNtOptions;
   extractNtOptions.AltStreams.Val = true; // change it!!!