[Bugfix] fix custom op GmmSwigluQuantWeightNzTensorList

[ChenxiQ]

What this PR does / why we need it?

1. Fixes the environment path used to locate custom op shared libraries.
2. Uses empty tensor initialization for op outputs instead of zero-initialization for better efficiency.

Does this PR introduce any user-facing change?

How was this patch tested?

• vLLM version: v0.11.2
• vLLM main: https://github.com/vllm-project/vllm/commit/v0.11.2

[gemini-code-assist]

Code Review

This pull request includes a bug fix and a performance optimization. In vllm_ascend/platform.py, a duplicated path segment in the construction of CUSTOM_OPP_PATH is corrected, which is a necessary fix. In csrc/torch_binding.cpp, at::zeros is replaced with at::empty for output tensor allocation, which is a good performance improvement. However, I've identified a related critical issue that should be addressed.

[gemini-code-assist]

The size of these output tensors depends on n, which is calculated on line 567 from the weight TensorList (weight[0].sizes()[1]). This is unsafe because if the weight TensorList is empty, accessing weight[0] will cause a crash. It's crucial to add a check to ensure weight is not empty before its elements are accessed.

For example, you could add the following check before line 567:

TORCH_CHECK(!weight.empty(), "weight tensor list cannot be empty");

[github-actions]

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