bug#26825: dired-do-compress should prompt with already determined action

[積丹尼 Dan Jacobson]

Z runs the command dired-do-compress

But it prompts
"Compress or uncompress local.osm.gz? (y or n)" y
Uncompressing /cf/updates/no_backup/local.osm.gz...done

Can't the test be done a little earlier, so we could get
"Uncompress local.osm.gz? (y or n)" y
Uncompressing /cf/updates/no_backup/local.osm.gz...done

I mean it checks at some point what it should do.
Can't it check before asking?
I suppose the only savings of not checking earlier is if the user
aborts, then no check is needed.

The mixed case prompt twin wording,
"Compress or uncompress [next 3 files]? (y or n)"
is only fully appropriate if there indeed is a mixed case involved.