Keep setting ret close to setting errp and don't merge different error
paths into one. This way it's more obvious that we don't return
error without setting errp.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Alberto Garcia <berto@igalia.com>
Message-Id: <20210202124956.63146-15-vsementsov@virtuozzo.com>
Signed-off-by: Eric Blake <eblake@redhat.com>