message [nfc]: Pull out _stripMatchFields helper for reconcileMessages

Author: chrisbobbe

lib/model/message.dart

@@ -426,13 +426,17 @@ class MessageStoreImpl extends HasChannelStore with MessageStore, _OutboxMessage
     for (int i = 0; i < messages.length; i++) {
       final message = messages[i];
       messages[i] = this.messages.putIfAbsent(message.id, () {
-        message.matchContent = null;
-        message.matchTopic = null;
-        return message;
+        return _stripMatchFields(message);
       });
     }
   }
 
+  Message _stripMatchFields(Message message) {
+    message.matchContent = null;
+    message.matchTopic = null;
+    return message;
+  }
+
   @override
   bool? getEditMessageErrorStatus(int messageId) {
     assert(!_disposed);