[bugfix][CI]Skip e2e log summary when the log file is missing or empty (#7552)

### What this PR does / why we need it?
Avoid failing `ci_log_summary.py` when the e2e log file is missing or
empty.

Test in CI
:https://github.com/vllm-project/vllm-ascend/actions/runs/23428406256/job/68149271871
### Does this PR introduce _any_ user-facing change?

### How was this patch tested?

- vLLM version: v0.18.0
- vLLM main:
8b6325758c

---------

Signed-off-by: Meihan-chen <jcccx.cmh@gmail.com>

.github/workflows/scripts/ci_log_summary.py

@@ -977,6 +977,8 @@ def main() -> None:
     if args.run_id is not None:
         result = process_run(args.run_id, repo=args.repo)
     else:
+        if not args.log_file.exists() or args.log_file.stat().st_size == 0:
+            return
         log_text = args.log_file.read_text(encoding="utf-8", errors="replace")
         result = process_local_log(log_text, job_name=args.step_name)