MAINT-8087: Use SHGetKnownFolderPath(), not SHGetSpecialFolderPath().

SHGetSpecialFolderPath() is deprecated, and empirically it appears to be
failing when the user name contains non-ASCII characters. The relevant
Microsoft documentation pages recommend calling SHGetKnownFolderPath()
instead.

Also, the SHGetSpecialFolderPath() calls had no error checking or reporting,
which is why we can only say it "appears to be" failing. Make sure that if
SHGetKnownFolderPath() fails, at least we try to tell somebody about it.

indra/llvfs/lldir_win32.cpp

@@ -31,7 +31,10 @@
 #include "lldir_win32.h"
 #include "llerror.h"
 #include "llrand.h"		// for gLindenLabRandomNumber
-#include "shlobj.h"
+#include <shlobj.h>
+#include <Knownfolders.h>
+#include <iostream>
+#include <map>
 
 #include <direct.h>
 #include <errno.h>
@@ -42,30 +45,59 @@
 #define PACKVERSION(major,minor) MAKELONG(minor,major)
 DWORD GetDllVersion(LPCTSTR lpszDllName);
 
+namespace {
+
+std::string getKnownFolderPath(const std::string& desc, REFKNOWNFOLDERID folderid)
+{
+    // https://msdn.microsoft.com/en-us/library/windows/desktop/bb762188(v=vs.85).aspx
+    PWSTR wstrptr = 0;
+    HRESULT result = SHGetKnownFolderPath(
+        folderid,
+        KF_FLAG_DEFAULT,            // no flags
+        NULL,                       // current user, no impersonation
+        &wstrptr);
+    if (result == S_OK)
+    {
+        std::string utf8 = utf16str_to_utf8str(llutf16string(wstrptr));
+        // have to free the returned pointer after copying its data
+        CoTaskMemFree(wstrptr);
+        return utf8;
+    }
+
+    // gack, no logging yet!
+    // at least say something to a developer trying to debug this...
+    static std::map<HRESULT, const char*> codes
+    {
+        { E_FAIL, "E_FAIL; known folder does not have a path?" },
+        { E_INVALIDARG, "E_INVALIDARG; not present on system?" }
+    };
+    auto found = codes.find(result);
+    const char* text = (found == codes.end())? "unknown" : found->second;
+    std::cout << "*** SHGetKnownFolderPath(" << desc << ") failed with "
+              << result << " (" << text << ")\n";
+    return {};
+}
+
+} // anonymous namespace
+
 LLDir_Win32::LLDir_Win32()
 {
 	mDirDelimiter = "\\";
 
-	WCHAR w_str[MAX_PATH];
-
 	// Application Data is where user settings go
-	SHGetSpecialFolderPath(NULL, w_str, CSIDL_APPDATA, TRUE);
-
-	mOSUserDir = utf16str_to_utf8str(llutf16string(w_str));
+	mOSUserDir = getKnownFolderPath("RoamingAppData", FOLDERID_RoamingAppData);
 
 	// We want cache files to go on the local disk, even if the
 	// user is on a network with a "roaming profile".
 	//
-	// On XP this is:
-	//   C:\Docments and Settings\James\Local Settings\Application Data
 	// On Vista this is:
 	//   C:\Users\James\AppData\Local
 	//
 	// We used to store the cache in AppData\Roaming, and the installer
 	// cleans up that version on upgrade.  JC
-	SHGetSpecialFolderPath(NULL, w_str, CSIDL_LOCAL_APPDATA, TRUE);
-	mOSCacheDir = utf16str_to_utf8str(llutf16string(w_str));
+	mOSCacheDir = getKnownFolderPath("LocalAppData", FOLDERID_LocalAppData);
 
+	WCHAR w_str[MAX_PATH];
 	if (GetTempPath(MAX_PATH, w_str))
 	{
 		if (wcslen(w_str))	/* Flawfinder: ignore */ 
@@ -73,6 +105,16 @@ LLDir_Win32::LLDir_Win32()
 			w_str[wcslen(w_str)-1] = '\0'; /* Flawfinder: ignore */ // remove trailing slash
 		}
 		mTempDir = utf16str_to_utf8str(llutf16string(w_str));
+
+		if (mOSUserDir.empty())
+		{
+			mOSUserDir = mTempDir;
+		}
+
+		if (mOSCacheDir.empty())
+		{
+			mOSCacheDir = mTempDir;
+		}
 	}
 	else
 	{