img.linuxfr.org should not redirect stylesheets if redirects img (circular dep)

cf. https://linuxfr.org/suivi/rendre-accessible-les-images-des-themes-sur-img-linuxfr-org

_images_ must be redirected from http://img.linuxfr.org to http://linuxfr.org because modified _stylesheets_ are hosted by http://img.linuxfr.org and _images_ are hosted by http://img.linuxfr.org . So we must not redirect _stylesheets_ because they are already where they should be.

It’s because _stylesheets_ are not redirected that we need to redirect _images_ and other assets.