fix: eliminate bad use-after-free(destroy) pattern (#1068)

* fix: eliminate bad use-after-free(destroy) pattern

* remove obsolete comment

Author: 0xFA11

com.unity.netcode.gameobjects/Runtime/Core/NetworkObject.cs

@@ -380,8 +380,20 @@ public static void NetworkHide(List<NetworkObject> networkObjects, ulong clientI
             }
         }
 
+        private bool m_ApplicationQuitting = false;
+
+        private void OnApplicationQuit()
+        {
+            m_ApplicationQuitting = true;
+        }
+
         private void OnDestroy()
         {
+            if (m_ApplicationQuitting)
+            {
+                return;
+            }
+
             if (NetworkManager != null && NetworkManager.IsListening && NetworkManager.IsServer == false && IsSpawned)
             {
                 throw new NotServerException($"Destroy a spawned {nameof(NetworkObject)} on a non-host client is not valid. Call {nameof(Destroy)} or {nameof(Despawn)} on the server/host instead.");

com.unity.netcode.gameobjects/Runtime/Spawning/NetworkSpawnManager.cs

@@ -685,8 +685,12 @@ internal void OnDespawnObject(NetworkObject networkObject, bool destroyGameObjec
                 }
             }
 
-            var gobj = networkObject.gameObject;
+            if (SpawnedObjects.Remove(networkObject.NetworkObjectId))
+            {
+                SpawnedObjectsList.Remove(networkObject);
+            }
 
+            var gobj = networkObject.gameObject;
             if (destroyGameObject && gobj != null)
             {
                 if (NetworkManager.PrefabHandler.ContainsHandler(networkObject))
@@ -698,14 +702,6 @@ internal void OnDespawnObject(NetworkObject networkObject, bool destroyGameObjec
                     UnityEngine.Object.Destroy(gobj);
                 }
             }
-
-            // for some reason, we can get down here and SpawnedObjects for this
-            //  networkId will no longer be here, even as we check this at the start
-            //  of the function
-            if (SpawnedObjects.Remove(networkObject.NetworkObjectId))
-            {
-                SpawnedObjectsList.Remove(networkObject);
-            }
         }
     }
 }