Fix null reference exception

Author: EmandM

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

@@ -3232,7 +3232,10 @@ internal void SynchronizeNetworkBehaviours<T>(ref BufferSerializer<T> serializer
                 {
                     reader.ReadValueSafe(out ushort networkBehaviourId);
                     var networkBehaviour = GetNetworkBehaviourAtOrderIndex(networkBehaviourId);
-                    networkBehaviour.Synchronize(ref serializer, targetClientId);
+                    if (networkBehaviour != null)
+                    {
+                        networkBehaviour.Synchronize(ref serializer, targetClientId);
+                    }
                 }
             }
         }

testproject/Assets/Tests/Runtime/Support/SpawnRpcDespawnInstanceHandler.cs

@@ -49,7 +49,7 @@ public NetworkObject Instantiate(ulong ownerClientId, Vector3 position, Quaterni
             {
                 if (NetworkLog.CurrentLogLevel <= LogLevel.Error)
                 {
-                    NetworkLog.LogError($"Failed to create object locally. [{nameof(m_PrefabHash)}={m_PrefabHash}]. {nameof(NetworkPrefab)} could not be found. Is the prefab registered with {nameof(NetworkManager)}?");
+                    NetworkLog.LogError($"[{nameof(m_PrefabHash)}={m_PrefabHash}] Failed to create object locally. {nameof(NetworkPrefab)} could not be found. Is the prefab registered with {nameof(NetworkManager)}?");
                 }
                 return null;
             }