xptracker: update lastXp after submitting xp gains

This prevents continious updates on logout after the threshold has been
reached.

Also initialize lastXp when the plugin starts in the event the player is
already logged in.

runelite-client/src/main/java/net/runelite/client/plugins/xptracker/XpTrackerPlugin.java

@@ -118,7 +118,7 @@ public class XpTrackerPlugin extends Plugin
 	private XpWorldType lastWorldType;
 	private String lastUsername;
 	private long lastTickMillis = 0;
-	private boolean fetchXp;
+	private boolean fetchXp; // fetch lastXp for the online xp tracker
 	private long lastXp = 0;
 
 	private final XpClient xpClient = new XpClient();
@@ -152,6 +152,9 @@ public class XpTrackerPlugin extends Plugin
 			.build();
 
 		clientToolbar.addNavigation(navButton);
+
+		// Initialize the last xp if already logged in
+		fetchXp = true;
 	}
 
 	@Override
@@ -206,6 +209,7 @@ public class XpTrackerPlugin extends Plugin
 			if (Math.abs(totalXp - lastXp) > XP_THRESHOLD)
 			{
 				xpClient.update(username);
+				lastXp = totalXp;
 			}
 		}
 	}