Encoding Issue for sitemapindex.xml

[BjarneWittlieb]

The SitemapIndex Controller does not specify an encoding and when visiting the sitemapindex in google chrome, a 500 response is generated.

Line 64 in GetaSitemapIndexController should be adjusted as follows:
return new FileContentResult(sitemapIndexData, "text/xml"); => return new FileContentResult(sitemapIndexData, "text/xml; charset=utf-8");