fix(nav): 发出新寻路请求时作废上一次最近可达点,避免跨目标读到过期数据

Assets/PathBerserker2d/Scripts/PathBerserker2d/NavAgent/NavAgent.cs

@@ -580,6 +580,8 @@ namespace PathBerserker2d
             currentPathRequest.start = currentMappedPosition;
             currentPathRequest.goals = goalPs;
             PBWorld.PathTo(currentPathRequest);
+            // 新请求发出 → 作废上一次的最近可达点(避免跨目标读到过期数据)；本次若失败会由 RaiseFailedToFindPath 重新写入。
+            _lastClosestReachable = NavSegmentPositionPointer.Invalid;
             traversedLinkSinceLastPath = false;
             return true;
         }