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

Adding comments about  getting the user name out of tyhe security principal in a file's DACL.

Author: John Dumais

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

@@ -168,6 +168,12 @@ 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) {
+                /*
+                If a file has no Windoze dacl entries, as may happen on a network-mounted file system, there won't 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.
+                 */
                 final String[] principalFields = aclEntry.principal().getName().split("\\\\");
 
                 if (principalFields.length < 2) {