Fix: Hunyuan model adding error. (#6531)

### What problem does this PR solve?

#6523
### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)

api/apps/llm_app.py

@@ -139,7 +139,7 @@ def add_llm():
     req = request.json
     factory = req["llm_factory"]
     api_key = req.get("api_key", "x")
-    llm_name = req["llm_name"]
+    llm_name = req.get("llm_name")
 
     def apikey_json(keys):
         nonlocal req