fix: show error messages as system and keep them in the message input (#319)

packages/stream_chat_flutter/lib/src/message_input.dart

@@ -2082,6 +2082,9 @@ class MessageInputState extends State<MessageInput> {
     }
 
     return sendingFuture.then((resp) {
+      if (resp.message?.type == 'error') {
+        _parseExistingMessage(message);
+      }
       if (widget.onMessageSent != null) {
         widget.onMessageSent(resp.message);
       }

packages/stream_chat_flutter/lib/src/message_list_view.dart

@@ -847,7 +847,8 @@ class _MessageListViewState extends State<MessageListView> {
     List<Message> messages,
     int index,
   ) {
-    if (message.type == 'system' && message.text?.isNotEmpty == true) {
+    if ((message.type == 'system' || message.type == 'error') &&
+        message.text?.isNotEmpty == true) {
       return widget.systemMessageBuilder?.call(context, message) ??
           SystemMessage(
             key: ValueKey<String>('MESSAGE-${message.id}'),