ade: Reject unknown arguments if they will not be used

Subcommands with no REMAINING arguments, such as "ade uninstall",
would previously accept and ignore unknown arguments. This could be
very bad if the command is something like "ade uninstall --dry-run".

Signed-off-by: Simon McVittie <smcv@collabora.com>
Reviewed-by: André Magalhães <andre.magalhaes@collabora.co.uk>
Differential Revision: https://phabricator.apertis.org/D6795