autocomplete: Use topic data from store in topic autocomplete

Author: sm-sayedi

lib/model/autocomplete.dart

@@ -6,7 +6,6 @@ import 'package:unorm_dart/unorm_dart.dart' as unorm;
 
 import '../api/model/events.dart';
 import '../api/model/model.dart';
-import '../api/route/channels.dart';
 import '../generated/l10n/zulip_localizations.dart';
 import '../widgets/compose_box.dart';
 import 'algorithms.dart';
@@ -1175,10 +1174,8 @@ class TopicAutocompleteView extends AutocompleteView<TopicAutocompleteQuery, Top
   Future<void> _fetch() async {
      assert(!_isFetching);
     _isFetching = true;
-    final result = await getStreamTopics(store.connection, streamId: streamId,
-      allowEmptyTopicName: true,
-    );
-    _topics = result.topics.map((e) => e.name);
+    await store.fetchTopics(streamId);
+    _topics = store.getChannelTopics(streamId)!.map((e) => e.name);
     _isFetching = false;
     return _startSearch();
   }