mcMMO no longer throws errors on below 0 xp gains

Fixes #4346

src/main/java/com/gmail/nossr50/runnables/database/UUIDUpdateAsyncTask.java

@@ -102,6 +102,7 @@ public class UUIDUpdateAsyncTask implements Runnable {
         if (position == userNames.size()) {
             mcMMO.getUpgradeManager().setUpgradeCompleted(UpgradeType.ADD_UUIDS);
             awaiter.countDown();
+            plugin.getLogger().info("UUID checks completed");
         } else
             this.runTaskLaterAsynchronously(plugin, Misc.TICK_CONVERSION_FACTOR * DELAY_PERIOD); // Schedule next batch
     }