File Browser: Improper Access Control Occurs via Pre-Created Public Share for a Non-existent Path

File Browser is a file managing interface for uploading, deleting, previewing, renaming, and editing files within a specified directory. Prior to 2.63.7, `POST /api/share/<path>` accepts an authenticated request for an arbitrary path and stores a public share record without checking whether the target file currently exists. Later, when a file is created at that same path, the previously created public share immediately becomes valid and exposes the new file through `GET /api/public/dl/<hash>`. This vulnerability is fixed in 2.63.7.