settings-widget: Fix crash when pairing is cancelled
When a pairing gets cancelled, we would try and turn off pairing for the devices in the device list, but the first child we'd hit isn't a row representing a device, but the placeholder for when there aren't any devices in that list.
GLib-GObject[16799]:CRITICAL: g_object_set_is_valid_property: object class 'GtkLabel' has no property named 'pairing'
Fixes: ba8bd8bd ("settings: Show a placeholder when the devices list is empty") Closes: #156 (closed)