Destroy cairo_font_options when done.

Change-Id: Ib49c07dee22fa59b4f6227c6b106a18b615aa060
Reviewed-on: https://gerrit.libreoffice.org/4193Reviewed-by: David Tardon <dtardon@redhat.com>
Tested-by: David Tardon <dtardon@redhat.com>