gpg: Allow --locate-external-key even with --no-auto-key-locate.

* g10/getkey.c (akl_empty_or_only_local): New.
* g10/gpg.c (DEFAULT_AKL_LIST): New.
(main): Use it here.
(main) <aLocateExtKeys>: Set default AKL if none is set.

This better matches the expectations of the user. The used list in
this case is the default list ("local,wkd") with local ignored by the
command anyway.

(cherry picked from commit d058d80ed0d5edeff6d85108054b1dfd45ddad7d)

• GnuPG-bug-id: T4662
• Signed-off-by: Werner Koch <wk@gnupg.org>