multimedia/libzen: Adjust package version

Upstream bundles libzen (named ZenLib upstream) both separately and
as a all-in-one bundle with mediainfo (multimedia/mediainfo) releases.
Libzen do not share the same versioning schema as mediainfo and hence
shouldn't use it. Upstream bundles snapshots of libzen however only
release versions are tracked (current version is defined as 0.4.41).
Current release bundle archive ships the latest commit of libzen
available and following Porters Handbook append commit date to
release version. Worth noting is that separate version provided
on upstream's download page corresponds to the tagged version on
GitHub.

Sources:
https://github.com/MediaArea/ZenLib
https://mediaarea.net/en/MediaInfo/Download/Source

PR: 276754
Approved by: portmgr (maintainer timeout, 1+ month)