Fix unfiledEntries not updating

If an roster push with a roster entry without any group is processed,
then the entry is not updated, because unfiledEntries.contains(entry)
would return true, as the RosterEntry.equals() method only compares the
name.

We simply fix it by always removing the entry first and then adding it
again.

Thanks to Christian Schudt for pointing this out.

SMACK-559

smack-core/src/main/java/org/jivesoftware/smack/Roster.java

@@ -702,9 +702,8 @@ public class Roster {
 
         // Mark the entry as unfiled if it does not belong to any groups.
         if (item.getGroupNames().isEmpty()) {
-            if (!unfiledEntries.contains(entry)) {
-                unfiledEntries.add(entry);
-            }
+            unfiledEntries.remove(entry);
+            unfiledEntries.add(entry);
         }
         else {
             unfiledEntries.remove(entry);