hw/uefi: check access for first variable

When listing variables (via get-next-variable-name) only the names of
variables which can be accessed will be returned.  That check was
missing for the first variable though.  Add it.

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Message-ID: <20250811130110.820958-3-kraxel@redhat.com>