fix(media): a shelf needs a name, so a mistagged chapter number parks

Plex's artist row for 272 chapters is a chapter number the ripper put in the
artist tag (0.4, 31, 05), which would have filed them under a shelf called 0.4.
A narrator is a person, so it must contain a letter; the same test is deliberately
not applied to a book title, which may honestly be 1984.

serverAppConfigs-docs/Dankserver/Media Relayout.md

@@ -352,9 +352,9 @@ Two laws are forced by what the rows actually hold:
 What it refuses, the music arm's list with one addition: a video container, audio
 no chapter row names, and a loose file in a folder holding two books all park under
 `_unsorted` with the path they have today — and so does a chapter whose row names
-**no book or no narrator**, placeholder included (`[Unknown Album]`, `no title`,
-`[Unknown Artist]`): unrelated books share those strings, so filing on one merges
-them. `Various Artists` is not a placeholder — that is a multi-cast read.
+**no book or no narrator**: a placeholder (`[Unknown Album]`, `[Unknown Artist]`)
+that unrelated books share, or a chapter number mistagged as the artist (`0.4`).
+`Various Artists` is not a placeholder — that is a multi-cast read.
 
 ## Laws