Fix NotificationChannel backup import.

We were recreating the channels before the database upgrade. We
have to do it after.

Fixes #8174

src/org/thoughtcrime/securesms/notifications/NotificationChannels.java

@@ -67,6 +67,26 @@ public class NotificationChannels {
     onCreate(context, notificationManager);
   }
 
+  /**
+   * Recreates all notification channels for contacts with custom notifications enabled. Should be
+   * safe to call repeatedly. Needs to be executed on a background thread.
+   */
+  @WorkerThread
+  public static void restoreContactNotificationChannels(@NonNull Context context) {
+    if (!NotificationChannels.supported()) {
+      return;
+    }
+
+    RecipientDatabase db = DatabaseFactory.getRecipientDatabase(context);
+
+    try (RecipientDatabase.RecipientReader reader = db.getRecipientsWithNotificationChannels()) {
+      Recipient recipient;
+      while ((recipient = reader.getNext()) != null) {
+        NotificationChannels.createChannelFor(context, recipient);
+      }
+    }
+  }
+
   /**
    * @return The channel ID for the default messages channel.
    */