Would this also be a bit better?

[aliveanyang]

	public class stbi__context
	{
		public byte[] _tempBuffer;
		public int img_n = 0;
		public int img_out_n = 0;
		public uint img_x = 0;
		public uint img_y = 0;

		private long _offset;

		public stbi__context(Stream stream)
		{
			if (stream == null)
				throw new ArgumentNullException("stream");

            _offset = stream.Position;
            Stream = stream;

        }

    public Stream Stream { get; }

        public long Seek(long offset, SeekOrigin origin)
        {
            if (origin == SeekOrigin.Begin)
            {
                return Stream.Seek(this._offset + offset, origin);
            }
            else
            {
                return Stream.Seek(offset, origin);
            }
        }
    }