File Browser: Incorrect access control in public directory shares via rule path rebasing

File Browser is a file managing interface for uploading, deleting, previewing, renaming, and editing files within a specified directory. Prior to 2.63.6, File Browser's public share handlers rebase the share owner's filesystem root to the shared directory and then evaluate descendant paths against the owner's global and per-user rules using the rebased relative path instead of the original path relative to the owner's scope. As a result, an attacker who knows a public directory share URL can access files and subdirectories that the owner explicitly blocked with rules, as long as those blocked paths are located underneath the shared directory. In the simplest case this is an unauthenticated information disclosure through `GET /api/public/share/*` and `GET /api/public/dl/*`. This vulnerability is fixed in 2.63.6.