Fix CVE-2026-32711
Path traversal in FileSet/DICOMDIR ReferencedFileID
allows file access outside the File-set root

[ Tests ]
autopkgtest are ok.

[ Checklist ]
  [*] *all* changes are documented in the d/changelog
  [*] I reviewed all changes and I approve them
  [*] attach debdiff against the package in (old)stable
  [*] the issue is verified as fixed in unstable

[ Changes ]
see attachment