Fix reconnections. This allows the main scene to be reloaded without

causing errors.

src/SpacetimeDBNetworkManager.cs

@@ -10,19 +10,19 @@ namespace SpacetimeDB
 	// Attach this to a gameobject in your scene to use SpacetimeDB.
 	public class SpacetimeDBNetworkManager : MonoBehaviour
 	{
-		private static bool _alreadyInitialized;
+		private static SpacetimeDBNetworkManager _instance;
 
 		public void Awake()
 		{
 			// Ensure that users don't create several SpacetimeDBNetworkManager instances.
 			// We're using a global (static) list of active connections and we don't want several instances to walk over it several times.
-			if (_alreadyInitialized)
+			if (_instance != null)
 			{
 				throw new InvalidOperationException("SpacetimeDBNetworkManager is a singleton and should only be attached once.");
 			}
 			else
 			{
-				_alreadyInitialized = true;
+				_instance = this;
 			}
 		}