community[patch]: callback before yield for mlx pipeline (#26928)

**Description:** Moves yield to after callback for `_stream` function
for the MLX pipeline model in the community llm package
**Issue:** #16913

libs/community/langchain_community/llms/mlx_pipeline.py

@@ -232,9 +232,9 @@ def _stream(
             # yield text, if any
             if text:
                 chunk = GenerationChunk(text=text)
-                yield chunk
                 if run_manager:
                     run_manager.on_llm_new_token(chunk.text)
+                yield chunk
 
             # break if stop sequence found
             if token == eos_token_id or (stop is not None and text in stop):