fix: don't destroy with owner not being honored when client exits (#3477)

Based on issue #3472, this PR resolves the issue where the
`NetworkObject.DontDestroyWithOwner` was not being honored.

<!-- Add short version of the JIRA ticket to the PR title (e.g. "feat:
new shiny feature [MTT-123]") -->

## Changelog

- Fixed: Issue where the `NetworkObject.DontDestroyWithOwner` was not
being honored.

## Testing and Documentation

- Includes integration test
`NetworkObjectDontDestroyWithOwnerTests.NetworkShowThenClientDisconnects`.
- No documentation changes or additions were necessary.


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- [ ] An `[Obsolete]` attribute was added along with a `(RemovedAfter
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## Backport
The v1.x branch does no have this issue, but went ahead and backported
the test in #3478.

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Author: NoelStephensUnity

com.unity.netcode.gameobjects/CHANGELOG.md

@@ -15,6 +15,7 @@ Additional documentation and release notes are available at [Multiplayer Documen
 
 ### Fixed
 
+- Fixed issue where the `NetworkObject.DontDestroyWithOwner` was not being honored. (#3477)
 - Fixed issue where non-authority `NetworkTransform` instances would not allow non-synchronized axis values to be updated locally. (#3471)
 - Fixed issue where invoking `NetworkObject.NetworkShow` and `NetworkObject.ChangeOwnership` consecutively within the same call stack location could result in an unnecessary change in ownership error message generated on the target client side. (#3468)
 - Fixed issue where `NetworkVariable`s on a `NetworkBehaviour` could fail to synchronize changes if one has `NetworkVariableUpdateTraits` set and is dirty but is not ready to send. (#3466)

com.unity.netcode.gameobjects/Runtime/Connection/NetworkConnectionManager.cs

@@ -1178,7 +1178,7 @@ internal void OnClientDisconnectFromServer(ulong clientId)
                     {
                         // If destroying with owner, then always despawn and destroy (or defer destroying to prefab handler)
                         // Handle an object with no observers other than the current disconnecting client as destroying with owner
-                        if (!ownedObject.DontDestroyWithOwner || ownedObject.Observers.Count == 0 || (ownedObject.Observers.Count == 1 && ownedObject.Observers.Contains(clientId)))
+                        if (!ownedObject.DontDestroyWithOwner && (ownedObject.Observers.Count == 0 || (ownedObject.Observers.Count == 1 && ownedObject.Observers.Contains(clientId))))
                         {
                             if (NetworkManager.PrefabHandler.ContainsHandler(ownedObject.GlobalObjectIdHash))
                             {
@@ -1244,7 +1244,7 @@ internal void OnClientDisconnectFromServer(ulong clientId)
                                     }
 
                                     // Skip destroy with owner objects as they will be processed by the outer loop
-                                    if (!childObject.DontDestroyWithOwner || childObject.Observers.Count == 0 || (childObject.Observers.Count == 1 && childObject.Observers.Contains(clientId)))
+                                    if (!childObject.DontDestroyWithOwner && (childObject.Observers.Count == 0 || (childObject.Observers.Count == 1 && childObject.Observers.Contains(clientId))))
                                     {
                                         continue;
                                     }

com.unity.netcode.gameobjects/Tests/Runtime/NetworkObject/NetworkObjectDontDestroyWithOwnerTests.cs

@@ -23,13 +23,19 @@ protected override bool UseCMBService()
         }
 
         protected GameObject m_PrefabToSpawn;
+        protected GameObject m_PrefabNoObserversSpawn;
 
         public NetworkObjectDontDestroyWithOwnerTests(HostOrServer hostOrServer) : base(hostOrServer) { }
 
         protected override void OnServerAndClientsCreated()
         {
             m_PrefabToSpawn = CreateNetworkObjectPrefab("ClientOwnedObject");
             m_PrefabToSpawn.GetComponent<NetworkObject>().DontDestroyWithOwner = true;
+
+            m_PrefabNoObserversSpawn = CreateNetworkObjectPrefab("NoObserversObject");
+            var prefabNoObserversNetworkObject = m_PrefabNoObserversSpawn.GetComponent<NetworkObject>();
+            prefabNoObserversNetworkObject.SpawnWithObservers = false;
+            prefabNoObserversNetworkObject.DontDestroyWithOwner = true;
         }
 
         [UnityTest]
@@ -74,5 +80,30 @@ public IEnumerator DontDestroyWithOwnerTest()
                 Assert.That(networkObject.OwnerClientId == m_ServerNetworkManager.LocalClientId);
             }
         }
+
+        [UnityTest]
+        public IEnumerator NetworkShowThenClientDisconnects()
+        {
+            var authorityManager = GetAuthorityNetworkManager();
+            var networkObject = SpawnObject(m_PrefabNoObserversSpawn, authorityManager).GetComponent<NetworkObject>();
+            var longWait = new WaitForSeconds(0.25f);
+            yield return longWait;
+            var nonAuthorityManager = GetNonAuthorityNetworkManager();
+            Assert.False(nonAuthorityManager.SpawnManager.SpawnedObjects.ContainsKey(networkObject.NetworkObjectId), $"[Client-{nonAuthorityManager.LocalClientId}] " +
+                $"Already has an instance of {networkObject.name} when it should not!");
+            networkObject.NetworkShow(nonAuthorityManager.LocalClientId);
+            networkObject.ChangeOwnership(nonAuthorityManager.LocalClientId);
+
+            yield return WaitForConditionOrTimeOut(() => nonAuthorityManager.SpawnManager.SpawnedObjects.ContainsKey(networkObject.NetworkObjectId)
+            && nonAuthorityManager.SpawnManager.SpawnedObjects[networkObject.NetworkObjectId].OwnerClientId == nonAuthorityManager.LocalClientId);
+            AssertOnTimeout($"[Client-{nonAuthorityManager.LocalClientId}] Failed to spawn {networkObject.name} when it was shown!");
+
+            yield return s_DefaultWaitForTick;
+
+            nonAuthorityManager.Shutdown();
+
+            yield return longWait;
+            Assert.True(networkObject.IsSpawned, $"The spawned test prefab was despawned on the authority side when it shouldn't have been!");
+        }
     }
 }