fix "keep_first_message" to make sure messages are in correct order, (#4653)

described in #3178 (comment)

Co-authored-by: Eric Zhu <[email protected]>

Author: milkmeat

autogen/agentchat/contrib/capabilities/transforms.py

@@ -96,7 +96,7 @@ def apply_transform(self, messages: List[Dict]) -> List[Dict]:
             if remaining_count == 1:
                 # If there's only 1 slot left and it's a 'tools' message, ignore it.
                 if messages[i].get("role") != "tool":
-                    truncated_messages.insert(1, messages[i])
+                    truncated_messages.insert(1 if self._keep_first_message else 0, messages[i])
 
             remaining_count -= 1
             if remaining_count == 0: