fix: Fixes player prefab hash serialization on IL2CPP

Author: TwoTenPvP

MLAPI/Configuration/NetworkConfig.cs

@@ -11,6 +11,13 @@
 
 namespace MLAPI.Configuration
 {
+    [Serializable]
+    internal class NullableBoolSerializable
+    {
+        [SerializeField]
+        public ulong Value;
+    }
+
     /// <summary>
     /// The configuration object used to start server, client and hosts
     /// </summary>
@@ -48,7 +55,7 @@ public class NetworkConfig
         /// The default player prefab
         /// </summary>
         [SerializeField]
-        internal ulong? PlayerPrefabHash;
+        internal NullableBoolSerializable PlayerPrefabHash;
         /// <summary>
         /// Whether or not a player object should be created by default. This value can be overriden on a case by case basis with ConnectionApproval.
         /// </summary>

MLAPI/Core/NetworkingManager.cs

@@ -303,7 +303,7 @@ private void OnValidate()
             }
             else
             {
-                NetworkConfig.PlayerPrefabHash = prefab.Hash;
+                NetworkConfig.PlayerPrefabHash.Value = prefab.Hash;
             }
         }