Fix for https://jira.spectralogic.com/browse/BPBROWSER-63

If a file has no dacl entries, as may happen on a network-mounted file system, there wont be a principal entry.  A principal is a combination of
security provider, like NT AUTHORITY, and user name, e.g. NT AUTHORITY\Gracie.  This code is looking for the user name -- the second half of the
principal.  With no principal, there is no second half of the principal.

Author: John Dumais

ds3-metadata/src/main/java/com/spectralogic/ds3client/metadata/WindowsMetadataStore.java

@@ -168,7 +168,14 @@ private void saveWindowsfilePermissions(final Path file) throws IOException {
             final StringBuilder userDisplayList = new StringBuilder();
             final Map<String, Set<Integer>> stringSetMap = new HashMap<>();
             for (final AclEntry aclEntry : aclEntries) {
-                userDisplay = aclEntry.principal().getName().split("\\\\")[1];
+                final String[] principalFields = aclEntry.principal().getName().split("\\\\");
+
+                if (principalFields.length < 2) {
+                    continue;
+                }
+
+                userDisplay = principalFields[1];
+
                 Set<Integer> newSet = stringSetMap.get(userDisplay);
                 aclEntryPermissions = aclEntry.permissions();
                 if (newSet == null) {