[Bugfix] Fix wrong computed_tokens when meet exception. (#6522)

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Fix wrong computed_tokens when meet exception. This pull request
addresses a bug in the KV transfer mechanism where an exception during
token lookup operations could lead to an incorrect count of
computed_tokens. By modifying the exception handling in both the lookup
and lookup_scheduler functions to return 0 instead of the start index,
the system now correctly indicates that no tokens were successfully
processed when a remote connection failure occurs. This enhancement
improves the robustness and accuracy of token management within the
vllm_ascend distributed KV pool.

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NO.

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Signed-off-by: xleoken <xleoken@163.com>

vllm_ascend/distributed/kv_transfer/kv_pool/ascend_store/pool_worker.py

@@ -572,7 +572,7 @@ class KVPoolWorker:
             # all tokens where found, return the maximal end
         except Exception as e:
             logger.error(f"Remote connection failed in contains: {e}")
-            return start
+            return 0
         return end
 
     def lookup_scheduler(
@@ -629,7 +629,7 @@ class KVPoolWorker:
         # all tokens where found, return the maximal end
         except Exception as e:
             logger.error(f"Remote connection failed in contains: {e}")
-            return start
+            return 0
         return end
 
     def check_all_layers_exists(self, res: list[int], num_layers: int) -> list[int]: