rootpath does nothing to absolute url() paths

Minimal Reproduction using less 3.12.0

fail.less:

.fail {
    background-image: url('/images/absolute.png');
}
.works {
    background-image: url('images/relative.png');
}

run:

lessc -rp=https://mycdn/url/folder fail.less ./out.css

out.css

.fail {
  background-image: url('/images/absolute.png');
}
.works {
  background-image: url('https://mycdn/url/folder/images/relative.png');
}

Why do I want this behavior?
During development the images are served by the local web server in the /images directory.
When publishing all static elements are served out of a folder on the CDN, the folder name is variable.
This is very similar to the issue reported in #2129 but that lacked the clear detail that the image url is absolute

Reproduce the issue with the provided fail.less file and lessc command, then trace how the -rp/--rootpath option handles relative and absolute url() values. Done means absolute URLs receive the configured rootpath while relative URLs retain their current behavior, with regression coverage for both examples.