refactor(core): move thread-conversation guard into _reloadChannelIfNeeded

Encapsulates the early-return conditions in one place so callers don't
need to know which contexts skip the reload.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: xsahil03x

packages/stream_chat_flutter_core/lib/src/message_list_core.dart

@@ -293,6 +293,10 @@ class MessageListCoreState extends State<MessageListCore> {
     // If the channel is up to date, we don't need to reload it.
     if (_upToDate) return;
 
+    // Thread conversations share the parent channel; reloading from a
+    // disposing thread would clobber the channel page state.
+    if (_isThreadConversation) return;
+
     try {
       return await _streamChannel?.reloadChannel();
     } catch (_) {
@@ -305,7 +309,7 @@ class MessageListCoreState extends State<MessageListCore> {
   @override
   void dispose() {
     _teardownController(widget.messageListController);
-    if (!_isThreadConversation) _reloadChannelIfNeeded();
+    _reloadChannelIfNeeded();
     super.dispose();
   }
 }