fix(core): move get currentChannels before async (#2138)

Author: renefloor

packages/stream_chat_flutter_core/CHANGELOG.md

@@ -6,6 +6,9 @@
   and directly working with the attachments list.
 - Added proper userAgent and systemEnvironment information for better diagnostics and analytics.
 
+🐞 Fixed
+- type '_$Loading<int, Channel>' is not a subtype of type 'Success<int, Channel>' in type cast [#1894](https://github.com/GetStream/stream-chat-flutter/issues/1894)
+
 ## 9.4.0
 
 - Updated minimum Flutter version to 3.27.4 for the SDK.

packages/stream_chat_flutter_core/lib/src/stream_channel_list_event_handler.dart

@@ -67,13 +67,13 @@ mixin class StreamChannelListEventHandler {
 
     if (channelId == null || channelType == null) return;
 
+    final currentChannels = [...controller.currentItems];
+
     final channel = await controller.getChannel(
       id: channelId,
       type: channelType,
     );
 
-    final currentChannels = [...controller.currentItems];
-
     final updatedChannels = [
       channel,
       ...currentChannels..removeWhere((it) => it.cid == channel.cid),