Invalidate ground items cache properly

Instead of clearing ground items after game state change, just mark the
ground items dirty.

Signed-off-by: Tomas Slusny <slusnucky@gmail.com>

runelite-client/src/main/java/net/runelite/client/plugins/grounditems/GroundItemsPlugin.java

@@ -195,8 +195,7 @@ public class GroundItemsPlugin extends Plugin
 	{
 		if (event.getGameState() == GameState.LOGGED_IN)
 		{
-			groundItems.clear();
-			collectedGroundItems.clear();
+			dirty = true;
 		}
 	}