test-qobject-input-visitor: Cover visit_type_uint64()

The new test demonstrates known bugs: integers between INT64_MAX+1 and
UINT64_MAX rejected, and integers between INT64_MIN and -1 are
accepted modulo 2^64.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <1490118290-6133-1-git-send-email-armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>