win: FAILED macro can't be used with HANDLE.

FAILED macro is for HRESULT, not for HANDLE.
FindFirstFile returns INVALID_HANDLE_VALUE when error or not found.
https://msdn.microsoft.com/library/windows/desktop/aa364418(v=vs.85).aspx

fixes #79

src/logging_unittest.cc

@@ -628,7 +628,7 @@ static void GetFiles(const string& pattern, vector<string>* files) {
     LOG(FATAL) << "No directory separator.";
   }
   const string dirname = pattern.substr(0, index + 1);
-  if (FAILED(handle)) {
+  if (handle == INVALID_HANDLE_VALUE) {
     // Finding no files is OK.
     return;
   }