Require an available notification manager at overlay IPC boundaries

tools/chatgui-android/app/src/main/java/com/utun/chat/data/RadioOverlayService.kt

@@ -59,7 +59,8 @@ class RadioOverlayService : Service() {
         fun refreshLanguage() {
             currentService?.let { service ->
                 service.createChannel()
-                service.getSystemService(NotificationManager::class.java).notify(NOTIF_ID, service.buildNotification())
+                requireNotNull(service.getSystemService(NotificationManager::class.java)) { "notification manager unavailable" }
+                    .notify(NOTIF_ID, service.buildNotification())
             }
         }
 
@@ -301,7 +302,7 @@ class RadioOverlayService : Service() {
             val ch = NotificationChannel(CHANNEL_ID, AppLanguage.text(R.string.radio_ptt), NotificationManager.IMPORTANCE_LOW).apply {
                 description = AppLanguage.text(R.string.radio_overlay_description)
             }
-            getSystemService(NotificationManager::class.java).createNotificationChannel(ch)
+            requireNotNull(getSystemService(NotificationManager::class.java)) { "notification manager unavailable" }.createNotificationChannel(ch)
         }
     }