[REG: 6.7->6.8] SVG file mime type not recognized if the file contains xml header

If the built-in Tika database is used, it says SVG files are are just xml files if the data contains <?xml version="1.0"?> header. They are now detected as application/xml instead of image/svg+xml like freedesktop does.

Because of that difference, trying to load SVG data as icons ends up using QPixmapIconEngine engine now which does not render them in high resolution for high DPI displays.