fix: ensure last step is reset when a quest is shut down

this ensures `panel.updateHighlight` is always called once when the quest is started

src/main/java/com/questhelper/managers/QuestManager.java

@@ -358,6 +358,8 @@ public void shutDownQuest(boolean shouldUpdateList)
 				selectedQuest = null;
 			}
 		}
+
+		this.lastStep = null;
 	}
 
 	public void activateShortestPath()