model: Remove unknown from UserTopicVisibilityPolicy

Author: Cairo09

lib/model/channel.dart

@@ -574,12 +574,9 @@ class ChannelStoreImpl extends HasUserStore with ChannelStore {
         if (channelFolder == null) return; // TODO(log)
 
         if (change.name != null) channelFolder.name = change.name!;
-        if (change.description != null)
-          channelFolder.description = change.description!;
-        if (change.renderedDescription != null)
-          channelFolder.renderedDescription = change.renderedDescription!;
-        if (change.isArchived != null)
-          channelFolder.isArchived = change.isArchived!;
+        if (change.description != null)  channelFolder.description = change.description!;
+        if (change.renderedDescription != null)  channelFolder.renderedDescription = change.renderedDescription!;
+        if (change.isArchived != null) channelFolder.isArchived = change.isArchived!;
 
       case ChannelFolderReorderEvent():
         final order = event.order;