Fix transfering ownership of a share to user with same id as receiver

When the ownership of a user share is transfered to the receiver the
share is removed, as the receiver now owns the original file. However,
due to a missing condition, any share with a group, link or remote with
the same id as the user was removed, not only the user shares.

Signed-off-by: Daniel Calviño Sánchez <danxuliu@gmail.com>