Fix NPE when attempting to stop a status-check for an unconfigured Quick Settings Tile

This app let’s you control your devices using Wake on Lan. Multiple devices can be configured in the app, which can later be controlled either from the app itself or from up to three Quick Settings Tiles. Each device’s online status is displayed in the list overview. The companion app for Wear OS let’s you control your devices directly from the watch. Anti-Features: NonFreeComp (the application includes non-free components): ⇒ The app contains libraries of Google Mobile Services, Android Wear, Firebase. NonFreeNet (this application promotes/depends a non-Free network service): ⇒ The app connects to Google servers (Firebase).