item charges: fix explorer's ring infobox caching

The infobox was being added each varbit change if the show infobox and show
explorer ring charges config settings were on. Introduced in
b89d535fcb

runelite-client/src/main/java/net/runelite/client/plugins/itemcharges/ItemChargePlugin.java

@@ -340,6 +340,7 @@ public class ItemChargePlugin extends Plugin
 		int explorerRingCharge = client.getVar(Varbits.EXPLORER_RING_ALCHS);
 		if (lastExplorerRingCharge != explorerRingCharge)
 		{
+			lastExplorerRingCharge = explorerRingCharge;
 			updateExplorerRingCharges(explorerRingCharge);
 		}
 	}