fixed late join bug

Author: Extrys

com.unity.netcode.gameobjects/Runtime/Spawning/NetworkPrefabHandler.cs

@@ -292,8 +292,9 @@ internal FastBufferReader GetInstantiationDataReader(uint objectHash, FastBuffer
             }
 
             fastBufferReader.ReadValueSafe(out int dataSize);
-            var dataReader = new FastBufferReader(fastBufferReader, Collections.Allocator.Temp, dataSize, fastBufferReader.Position);
-            fastBufferReader.Seek(dataSize);
+            var position = fastBufferReader.Position;
+            var dataReader = new FastBufferReader(fastBufferReader, Collections.Allocator.Temp, dataSize, position);
+            fastBufferReader.Seek(position + dataSize);
             return dataReader;
         }