fix: Dynamically spawned NetworkObject throws exception due to no scene of origin handle [MTT-3852] (#2017)

Author: NoelStephensUnity

com.unity.netcode.gameobjects/CHANGELOG.md

@@ -20,6 +20,7 @@ Additional documentation and release notes are available at [Multiplayer Documen
 ### Removed
 
 ### Fixed
+- Fixed issue where dynamically spawned `NetworkObject`s could throw an exception if the scene of origin handle was zero (0) and the `NetworkObject` was already spawned. (#2017)
 - Fixed issue where `NetworkObject.Observers` was not being cleared when despawned. (#2009)
 - Fixed `NetworkAnimator` could not run in the server authoritative mode. (#2003)
 - Fixed issue where late joining clients would get a soft synchronization error if any in-scene placed NetworkObjects were parented under another `NetworkObject`. (#1985)

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

@@ -221,8 +221,7 @@ internal Scene SceneOrigin
         /// </summary>
         internal int GetSceneOriginHandle()
         {
-            // Sanity check to make sure nothing
-            if (SceneOriginHandle == 0 && IsSpawned)
+            if (SceneOriginHandle == 0 && IsSpawned && IsSceneObject != false)
             {
                 throw new Exception($"{nameof(GetSceneOriginHandle)} called when {nameof(SceneOriginHandle)} is still zero but the {nameof(NetworkObject)} is already spawned!");
             }

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

@@ -168,6 +168,23 @@ bool HasConditionBeenMet()
             Assert.False(s_GlobalTimeoutHelper.TimedOut, "Timed out while waiting for client side despawns! (2nd pass)");
         }
 
+        [Test]
+        public void DynamicallySpawnedNoSceneOriginException()
+        {
+            var gameObject = new GameObject();
+            var networkObject = gameObject.AddComponent<NetworkObject>();
+            networkObject.IsSpawned = true;
+            networkObject.SceneOriginHandle = 0;
+            networkObject.IsSceneObject = false;
+            // This validates invoking GetSceneOriginHandle will not throw an exception for a dynamically spawned NetworkObject
+            // when the scene of origin handle is zero
+            var sceneOriginHandle = networkObject.GetSceneOriginHandle();
+
+            // This validates that GetSceneOriginHandle will return the GameObject's scene handle that should be the currently active scene
+            var activeSceneHandle = UnityEngine.SceneManagement.SceneManager.GetActiveScene().handle;
+            Assert.IsTrue(sceneOriginHandle == activeSceneHandle, $"{nameof(NetworkObject)} should have returned the active scene handle of {activeSceneHandle} but returned {sceneOriginHandle}");
+        }
+
         private class TrackOnSpawnFunctions : NetworkBehaviour
         {
             public int OnNetworkSpawnCalledCount { get; private set; }