Fixed incorrect logic in another XmlReader's example

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Code sample in these articles:

https://learn.microsoft.com/en-us/dotnet/standard/linq/stream-xml-fragments-access-header-information
https://learn.microsoft.com/en-us/dotnet/standard/linq/perform-streaming-transform-large-xml-documents

suffers from the same issue described in #43799 - it only works when the input XML contains formatting.

Here is the fixed code.

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Internal previews

📄 File	🔗 Preview link
docs/standard/linq/perform-streaming-transform-large-xml-documents.md	How to perform streaming transform of large XML documents (LINQ to XML)
docs/standard/linq/stream-xml-fragments-access-header-information.md	How to stream XML fragments with access to header information - LINQ to XML

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Ping.