PipeTable invalid rendering

Hi,

Given table is rendered as below.

var content = File.ReadAllText("source.md");

var pipeline = new MarkdownPipelineBuilder()
    .UseAdvancedExtensions()
    .UseGridTables()
    .UsePipeTables()
    .EnableTrackTrivia()
    .Build();

var document = Markdown.Parse(content, pipeline);

using var sw = new StringWriter();
var renderer = new RoundtripRenderer(sw);
var output = renderer.Render(document).ToString();

File.WriteAllText("modified.md", output);

| Column 1 | Column 2 |
|----------|----------|
| Test     | Test 2   |
| Test     | Test 2   |

Column 1Column 2TestTest 2TestTest 2

Start with the supplied C# reproduction, focusing on the Markdown.Parse pipeline with UsePipeTables and the RoundtripRenderer. Compare the rendered output with the input table and trace how the parsed pipe-table structure is handled; done means the round-trip output preserves the table rows and columns.