community[patch]: Invoke callback prior to yielding token fix [Huggin…

…gFaceTextGenInference] (#20426)

…gFaceTextGenInference)

- [x] **PR title**: community[patch]: Invoke callback prior to yielding
token fix for [HuggingFaceTextGenInference]


- [x] **PR message**: 
- **Description:** Invoke callback prior to yielding token in stream
method in [HuggingFaceTextGenInference]
    - **Issue:** #16913
    - **Dependencies:** None
    - **Twitter handle:** @bolun_zhang

If no one reviews your PR within a few days, please @-mention one of
baskaryan, efriis, eyurtsev, hwchase17.

---------

Co-authored-by: Chester Curme <[email protected]>

libs/community/langchain_community/llms/huggingface_text_gen_inference.py

@@ -259,9 +259,10 @@ 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 stop_seq_found:
@@ -295,9 +296,10 @@ async def _astream(
             # yield text, if any
             if text:
                 chunk = GenerationChunk(text=text)
-                yield chunk
+
                 if run_manager:
                     await run_manager.on_llm_new_token(chunk.text)
+                yield chunk
 
             # break if stop sequence found
             if stop_seq_found: