Allow Optional Inclusion of `xl/theme/theme1.xml` to Avoid Invalid XLSX Detection

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I understand that the xl/theme/theme1.xml file is not a mandatory component of an XLSX file, but is there any room to make it optionally includable?

In some file filtering services, if an XLSX file lacks the xl/theme/theme1.xml file, it is mistakenly flagged as an invalid XLSX file.