[Bugfix] Add the check for a null VllmConfig

[gcanlin]

What this PR does / why we need it?

In vllm-omni, we create the empty VllmConfig, which raised the null error in vllm-ascend/vllm_ascend/utils.py. More details are here.

Does this PR introduce any user-facing change?

How was this patch tested?

• vLLM version: v0.12.0
• vLLM main: vllm-project/vllm@ad32e3e

[gemini-code-assist]

Code Review

This pull request adds a null check for vllm_config in the is_vl_model function to prevent a potential AttributeError. The change is correct and improves the robustness of the code. However, the fix is incomplete as it doesn't check for vllm_config.model_config.hf_config before use, which could still lead to an AttributeError. I've added a comment with a suggestion to make the check more comprehensive. Additionally, a similar issue exists in the is_moe_model function which could also be addressed for consistency.

[github-actions]

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