Fix an IndexOutOfBoundsException: Index: 0

In SaveTimerTask.java

Fixes #2039

src/main/java/com/gmail/nossr50/util/player/UserManager.java

@@ -62,8 +62,10 @@ public final class UserManager {
         Collection<McMMOPlayer> playerCollection = new ArrayList<McMMOPlayer>();
 
         for (Player player : mcMMO.p.getServer().getOnlinePlayers()) {
+            if (hasPlayerDataKey(player)) {
                 playerCollection.add(getPlayer(player));
             }
+        }
 
         return playerCollection;
     }