Check for null keys in settings view model

The keys to format in the settings view model might be null. This avoid crashing
the UI by testing for this case.

src/domain/session/settings/SettingsViewModel.js

@@ -28,6 +28,9 @@ class PushNotificationStatus {
 }
 
 function formatKey(key) {
+    if (!key) {
+        return null;
+    }
     const partLength = 4;
     const partCount = Math.ceil(key.length / partLength);
     let formattedKey = "";