Protect against asciidoc headers (#843)

Mpdreamz · web-flow · commit 52702d5ed041 · 2025-03-25T16:22:46.000+01:00
```
[source,esql]
----
```
diff --git a/src/Elastic.Markdown/IO/MarkdownFile.cs b/src/Elastic.Markdown/IO/MarkdownFile.cs
@@ -281,6 +281,7 @@ public static List<PageTocItem> GetAnchors(
 			.Descendants<HeadingBlock>()
 			.Where(block => block is { Level: >= 2 })
 			.Select(h => (h.GetData("header") as string, h.GetData("anchor") as string, h.Level))
+			.Where(h => h.Item1 is not null)
 			.Select(h =>
 			{
 				var header = h.Item1!.StripMarkdown();

Original file line number	Diff line number	Diff line change
`@@ -281,6 +281,7 @@ public static List<PageTocItem> GetAnchors(`
`281`	`281`	`.Descendants<HeadingBlock>()`
`282`	`282`	`.Where(block => block is { Level: >= 2 })`
`283`	`283`	`.Select(h => (h.GetData("header") as string, h.GetData("anchor") as string, h.Level))`
	`284`	`+ .Where(h => h.Item1 is not null)`
`284`	`285`	`.Select(h =>`
`285`	`286`	`{`
`286`	`287`	`var header = h.Item1!.StripMarkdown();`