fix userConnection initialization issue (Azure#33140)

* fix userConnection initialization issue

fix userConnection initialization issue when using callfack in simulator
of gen SDK.

* add config chk when converting cfg to openai model

Author: qusongms

sdk/ai/azure-ai-generative/azure/ai/generative/synthetic/simulator/simulator/simulator.py

@@ -38,6 +38,8 @@ def __init__(
         self.simulate_callback = simulate_callback
 
     def _to_openai_chat_completion_model(self, config: "AzureOpenAIModelConfiguration"):
+        if config == None:
+            return None
         token_manager = PlainTokenManager(
             openapi_key=config.api_key,
             auth_header="api-key",