Make sure Firebase crash does not crash the app or coroutine

app/src/play/java/io/heckel/ntfy/firebase/FirebaseMessenger.kt

@@ -5,21 +5,29 @@ import io.heckel.ntfy.log.Log
 
 class FirebaseMessenger {
     fun subscribe(topic: String) {
-        FirebaseMessaging
-            .getInstance()
+        val firebase = maybeInstance() ?: return
+        firebase
             .subscribeToTopic(topic)
             .addOnCompleteListener {
                 Log.d(TAG, "Subscribing to topic $topic complete: result=${it.result}, exception=${it.exception}, successful=${it.isSuccessful}")
             }
-            .addOnFailureListener {
-                Log.e(TAG, "Subscribing to topic $topic failed: $it")
+            .addOnFailureListener { e ->
+                Log.e(TAG, "Subscribing to topic $topic failed: ${e.message}", e)
             }
     }
 
     fun unsubscribe(topic: String) {
-        FirebaseMessaging
-            .getInstance()
-            .unsubscribeFromTopic(topic)
+        val firebase = maybeInstance() ?: return
+        firebase.unsubscribeFromTopic(topic)
+    }
+
+    private fun maybeInstance(): FirebaseMessaging? {
+        return try {
+            FirebaseMessaging.getInstance()
+        } catch (e: Exception) {
+            Log.e(TAG, "Firebase instance unavailable: ${e.message}", e)
+            null
+        }
     }
 
     companion object {