During calculation of the quality index of the image, we should
take into account also SVM vector image type.
Its mime type is image/x-vclgraphic.

Change-Id: I7c723e99995f73258bb59d976a6c7670c51f7a25
Reviewed-on: https://gerrit.libreoffice.org/51599Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Samuel Mehrbrodt <Samuel.Mehrbrodt@cib.de>