fix: improve lastMessageAt update logic

Author: xsahil03x

packages/stream_chat/lib/src/client/channel.dart

@@ -3537,12 +3537,10 @@ class ChannelClientState {
 
     // Calculate the new last message at time.
     var lastMessageAt = _channelState.channel?.lastMessageAt;
-    final lastMessage = updatedChannelMessages.lastWhereOrNull(
-      _shouldUpdateChannelLastMessageAt,
-    );
-
-    if (lastMessage != null) {
-      lastMessageAt = [lastMessageAt, lastMessage.createdAt].nonNulls.max;
+    for (final message in affectedMessages) {
+      if (_shouldUpdateChannelLastMessageAt(message)) {
+        lastMessageAt = [lastMessageAt, message.createdAt].nonNulls.max;
+      }
     }
 
     _channelState = _channelState.copyWith(