gpg: Allow overridden key import when stub exists.
* g10/import.c (do_transfer): Force importing when it's card reference.
Cherry-picked from 2.4 branch:
2c1297055041b4657ea1a927acac978c2b09a483
- GnuPG-bug-id: T3456
- Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>