Album import tries to search even if artist and album are missing

Tracks without empfy album information are tried to be grouped together in an album which leads to useless search results.

### Problem

Running this command:

```sh
$ beet import -t -g /remote/data/music-archive/DrumnbassJungleDrumfunk/0-Single-Tracks/Crossfire

/remote/data/music-archive/DrumnbassJungleDrumfunk/0-Single-Tracks/Crossfire/crossfire - Battlefield.mp3
/remote/data/music-archive/DrumnbassJungleDrumfunk/0-Single-Tracks/Crossfire/Crossfire - Firebolt.mp3
/remote/data/music-archive/DrumnbassJungleDrumfunk/0-Single-Tracks/Crossfire/Crossfire - Hydra (Cell D Rmx)-2.mp3
/remote/data/music-archive/DrumnbassJungleDrumfunk/0-Single-Tracks/Crossfire/Crossfire - Lethal formz.mp3
/remote/data/music-archive/DrumnbassJungleDrumfunk/0-Single-Tracks/Crossfire/Crossfire - Nightscape.mp3
/remote/data/music-archive/DrumnbassJungleDrumfunk/0-Single-Tracks/Crossfire/Crossfire - Sword Fight.mp3
/remote/data/music-archive/DrumnbassJungleDrumfunk/0-Single-Tracks/Crossfire/Crossfire_-_Northern_Lightz.mp3 (7 items)
Finding tags for album " - ".
Candidates:
1. Marco Wellisch - Shambakla (30.7%) (tracks, album, artist, ...) (Beatport, Digital, 2021, Moehre Rekorder, MORE009)
2. Issam Ogur - Antares (29.0%) (album, artist, tracks, ...) (Beatport, Digital, 2022, Krad Records, KRD380)
3. aetos - Symphonies Of December (17.7%) (album, artist, unmatched tracks, ...) (Beatport, Digital, 2021, recordJet, RLS00178501)
4. Charmes - Doing To Me (15.5%) (unmatched tracks, album, artist, ...) (Beatport, Digital, 2022, IN CONTROL RECORDINGS, ICR056)
5. Fanfickk - Feel Better (Waker Remix) (15.3%) (unmatched tracks, album, artist, ...) (Beatport, Digital, 2021, recordJet, RLS00177899)
# selection (default 1), Skip, Use as-is, as Tracks, Group albums,
Enter search, enter Id, aBort, eDit, edit Candidates, plaY?
```

It seems the reason that `--group-albums` tries to find an album for all these tracks is that they share the same information in the album tag: Nothing/Empfy as well as in the artist tag: Nothing/Empty

### Proposed solution

A warning could be thrown at the user that since we are dealing with insufficient information, it does not make sense to search any api.

Also the only useful thing at this prompt for a user to do is to either change to singelton mode, or to group these albums together in a "pseudo album", named something like "Album Unknown" and then try to reimport those files later on. This could somehow also be thrown at the user instead of uselessly searching an api.

### Setup

* OS: Manjaro
* Python version: 3.10.8
* beets version: 1.6.1 git-master
* Turning off plugins made problem go away: no

My configuration (output of `beet config`) is:

- I'll post a longish config once we decide it would help.

Start by reproducing the reported `beet import -t -g` command with tracks whose artist and album tags are empty, then trace the import grouping and search flow. Done should mean these tracks no longer produce a useless API search and instead receive the user-facing handling described in the issue.

Written by the indexing model from the issue text.