trivial: fu-udev-device: fix some assertions
trivial: fu-udev-device: fix some assertions

These seem to be caused by udev_parent being `NULL`.

```
19:26:06:0220 GLib-GObject         g_object_ref: assertion 'G_IS_OBJECT (object)' failed
19:26:06:0220 GUdev                g_udev_device_get_property: assertion 'G_UDEV_IS_DEVICE (device)' failed
19:26:06:0220 GUdev                g_udev_device_get_parent: assertion 'G_UDEV_IS_DEVICE (device)' failed
19:26:06:0221 GLib-GObject         g_object_ref: assertion 'G_IS_OBJECT (object)' failed
19:26:06:0221 GUdev                g_udev_device_get_property: assertion 'G_UDEV_IS_DEVICE (device)' failed
19:26:06:0221 GUdev                g_udev_device_get_parent: assertion 'G_UDEV_IS_DEVICE (device)' failed
19:26:06:0221 GLib-GObject         g_object_ref: assertion 'G_IS_OBJECT (object)' failed
19:26:06:0221 GUdev                g_udev_device_get_property: assertion 'G_UDEV_IS_DEVICE (device)' failed
19:26:06:0221 GUdev                g_udev_device_get_parent: assertion 'G_UDEV_IS_DEVICE (device)' failed
19:26:06:0222 GLib-GObject         g_object_ref: assertion 'G_IS_OBJECT (object)' failed
19:26:06:0222 GUdev                g_udev_device_get_property: assertion 'G_UDEV_IS_DEVICE (device)' failed
19:26:06:0222 GUdev                g_udev_device_get_parent: assertion 'G_UDEV_IS_DEVICE (device)' failed
19:26:06:0222 GLib-GObject         g_object_ref: assertion 'G_IS_OBJECT (object)' failed
19:26:06:0222 GUdev                g_udev_device_get_property: assertion 'G_UDEV_IS_DEVICE (device)' failed
19:26:06:0222 GUdev                g_udev_device_get_parent: assertion 'G_UDEV_IS_DEVICE (device)' failed
19:26:06:0222 GLib-GObject         g_object_ref: assertion 'G_IS_OBJECT (object)' failed
19:26:06:0222 GUdev                g_udev_device_get_property: assertion 'G_UDEV_IS_DEVICE (device)' failed
19:26:06:0222 GUdev                g_udev_device_get_parent: assertion 'G_UDEV_IS_DEVICE (device)' failed
19:26:06:0223 GLib-GObject         g_object_ref: assertion 'G_IS_OBJECT (object)' failed
19:26:06:0223 GUdev                g_udev_device_get_property: assertion 'G_UDEV_IS_DEVICE (device)' failed
19:26:06:0223 GUdev                g_udev_device_get_parent: assertion 'G_UDEV_IS_DEVICE (device)' failed
19:26:06:0223 GLib-GObject         g_object_ref: assertion 'G_IS_OBJECT (object)' failed
19:26:06:0223 GUdev                g_udev_device_get_property: assertion 'G_UDEV_IS_DEVICE (device)' failed
19:26:06:0223 GUdev                g_udev_device_get_parent: assertion 'G_UDEV_IS_DEVICE (device)' failed
19:26:06:0224 GLib-GObject         g_object_ref: assertion 'G_IS_OBJECT (object)' failed
19:26:06:0224 GUdev                g_udev_device_get_property: assertion 'G_UDEV_IS_DEVICE (device)' failed
19:26:06:0224 GUdev                g_udev_device_get_parent: assertion 'G_UDEV_IS_DEVICE (device)' failed
19:26:06:0224 GLib-GObject         g_object_ref: assertion 'G_IS_OBJECT (object)' failed
19:26:06:0224 GUdev                g_udev_device_get_property: assertion 'G_UDEV_IS_DEVICE (device)' failed
19:26:06:0224 GUdev                g_udev_device_get_parent: assertion 'G_UDEV_IS_DEVICE (device)' failed
19:26:06:0225 GLib-GObject         g_object_ref: assertion 'G_IS_OBJECT (object)' failed
19:26:06:0225 GUdev                g_udev_device_get_property: assertion 'G_UDEV_IS_DEVICE (device)' failed
19:26:06:0225 GUdev                g_udev_device_get_parent: assertion 'G_UDEV_IS_DEVICE (device)' failed
19:26:06:0225 GLib-GObject         g_object_ref: assertion 'G_IS_OBJECT (object)' failed
19:26:06:0225 GUdev                g_udev_device_get_property: assertion 'G_UDEV_IS_DEVICE (device)' failed
19:26:06:0225 GUdev                g_udev_device_get_parent: assertion 'G_UDEV_IS_DEVICE (device)' failed
19:26:06:0225 GLib-GObject         g_object_ref: assertion 'G_IS_OBJECT (object)' failed
19:26:06:0225 GUdev                g_udev_device_get_property: assertion 'G_UDEV_IS_DEVICE (device)' failed
19:26:06:0226 GUdev                g_udev_device_get_parent: assertion 'G_UDEV_IS_DEVICE (device)' failed
19:26:06:0226 GLib-GObject         g_object_ref: assertion 'G_IS_OBJECT (object)' failed
19:26:06:0226 GUdev                g_udev_device_get_property: assertion 'G_UDEV_IS_DEVICE (device)' failed
19:26:06:0226 GUdev                g_udev_device_get_parent: assertion 'G_UDEV_IS_DEVICE (device)' failed
19:26:06:0226 GLib-GObject         g_object_ref: assertion 'G_IS_OBJECT (object)' failed
19:26:06:0226 GUdev                g_udev_device_get_property: assertion 'G_UDEV_IS_DEVICE (device)' failed
19:26:06:0226 GUdev                g_udev_device_get_parent: assertion 'G_UDEV_IS_DEVICE (device)' failed
19:26:06:0227 GLib-GObject         g_object_ref: assertion 'G_IS_OBJECT (object)' failed
19:26:06:0227 GUdev                g_udev_device_get_property: assertion 'G_UDEV_IS_DEVICE (device)' failed
19:26:06:0227 GUdev                g_udev_device_get_parent: assertion 'G_UDEV_IS_DEVICE (device)' failed
```

fwupd/fwupd,fwupd/fwupd,hughsie/fwupd,fwupd/fwupd,hughsie/fwupd,hughsie/fwupd,fwupd/fwupd,hughsie/fwupd