mounts: say nothing an entry of sources holds when it cannot be read

A password typed into an entry by mistake, in another scheme or split by a
space or a comma, was quoted back in the problem and so reached the status
and the health answer. An entry is now named by its source's name or its
position only; a user with a control character or a second @ is refused
(review of mesh-catalog#190, issue 386).

modules/mounts/README.md

@@ -66,11 +66,12 @@ Both are preferences whose default, `none`, names nothing (ADR 0262 allows no em
   For example `library=/srv/library downloads=/srv/downloads:ro`.
 - `sources`: space-separated occasional sources, each optionally `:ro`:
   `name=smb://[<user>@]<host>/<share>@<mountpoint>` or `name=disk:<filesystem uuid>@<mountpoint>`.
-  For example `games=smb://root@192.0.2.76/Share@/mnt/games`. An SMB source's username is in its entry: it
-  is not a secret (novox/hq ADR 0283). It is percent-decoded, so a device that needs a domain takes it as
+  For example `games=smb://root@192.0.2.76/Share@/mnt/games`; the host is a name or an IPv4 address. An SMB
+  source's username is in its entry: it is not a secret (novox/hq ADR 0283). It is percent-decoded, so a device that needs a domain takes it as
   `WORKGROUP%5Cuser` (for `WORKGROUP\user`), and an `@` in it is written `%40`; it holds no space, comma or
   `=`. A password never goes in the entry: `user:password@` is refused, saying so and never what was
-  written. An SMB entry that cannot be read is said without what it holds.
+  written. An entry that cannot be read is said by its source's name, or by its position when even the name
+  cannot be read, and never with what it holds.
 
 A mount point is an absolute, plainly written path, not a directory of the system's own (`/etc`, `/usr`,
 `/run`, …). An entry that cannot be read is said, and only that entry is left out.