[bugfix][main]fix proxy decode bug (#3750)

### What this PR does / why we need it?

fix proxy decode bug when parsing non-UTF-8 characters.

- vLLM version: v0.11.0
- vLLM main:
c9461e05a4

---------

Signed-off-by: CHEN <116010019@link.cuhk.edu.cn>

examples/disaggregated_prefill_v1/load_balance_proxy_layerwise_server_example.py

@@ -556,7 +556,13 @@ async def _handle_completions(api: str, request: Request):
                                 instance_info.prefiller_idx,
                                 instance_info.prefiller_score)
                             released_kv = True
-                        chunk_str = chunk.decode("utf-8").strip()
+                        try:
+                            chunk_str = chunk.decode("utf-8").strip()
+                        except UnicodeDecodeError:
+                            logger.debug(
+                                f"Skipping chunk: {chunk}")
+                            yield chunk
+                            continue
                         if not chunk_str:
                             continue
                         if chunk_str.startswith("data: "):

examples/disaggregated_prefill_v1/load_balance_proxy_server_example.py

@@ -539,7 +539,13 @@ async def _handle_completions(api: str, request: Request):
                                 instance_info.prefiller_idx,
                                 instance_info.prefiller_score)
                             released_kv = True
-                        chunk_str = chunk.decode("utf-8").strip()
+                        try:
+                            chunk_str = chunk.decode("utf-8").strip()
+                        except UnicodeDecodeError:
+                            logger.debug(
+                                f"Skipping chunk: {chunk}")
+                            yield chunk
+                            continue
                         if not chunk_str:
                             continue
                         if chunk_str.startswith("data: "):