Invert validity check for IIIF URL
Invert validity check for IIIF URL

Makes the "success" case the one that gets to the bottom of the
function, which just feels more correct

uoregon-libraries/rais-image-server,uoregon-libraries/rais-image-server,uoregon-libraries/rais-image-server,uoregon-libraries/rais-image-server