Error creating thumbnail: convert: improper image header `/var/www/wiki.documentfoundation.org/images/c/c8/10_20_releases.xcf' @ error/xcf.c/ReadXCFImage/1316. convert: no images defined `/var/www/wiki.documentfoundation.org/images/tmp/transform_fb2d120e2c47.png' @ error/convert.c/ConvertImageCommand/3229. Error code: 1