copyparty: Sharing a single file does not fully restrict access to other files in source folder

Copyparty is a portable file server. In versions prior to 1.19.8, there was a missing permission-check in the shares feature (the `shr` global-option). When a share was created for just one file inside a folder, it was possible to access the other files inside that folder by guessing the filenames. It was not possible to descend into subdirectories in this manner; only the sibling files were accessible. This issue did not affect filekeys or dirkeys. Version 1.19.8 fixes the issue.