community[patch]: Invoke on_llm_new_token callback before yielding ch…

…unk (#24938)

**Description**: Invoke on_llm_new_token callback before yielding chunk
in streaming mode
**Issue**:
[#16913](#16913)

libs/community/langchain_community/chat_models/mlx.py

@@ -186,9 +186,9 @@ def _stream(
             # yield text, if any
             if text:
                 chunk = ChatGenerationChunk(message=AIMessageChunk(content=text))
-                yield chunk
                 if run_manager:
                     run_manager.on_llm_new_token(text, chunk=chunk)
+                yield chunk
 
             # break if stop sequence found
             if token == eos_token_id or (stop is not None and text in stop):