gpg: Fix testing for secret key availability.

* g10/getkey.c (have_secret_key_with_kid): Do not change the search
mode.

The search mode was accidentally changed to search-next after finding
the first keyblock. The intention was to look for a duplicate keyid
in the keydb which works by not doing a keydb_search_reset.

• Signed-off-by: Werner Koch <wk@gnupg.org>