keybox: Fix the not yet used uid and pk keyblock index return values.

* kbx/backend-sqlite.c (be_sqlite_search): Return pk_no and uid_no
without an offset of 1.

Probably to distinguish between error and unknown value the values
which returned the UID or subkey which was used to find that item were
one off. This is confusing and does not match the documentation.
Easy to fix because they were not yet used.