fix: handle NotGiven from from_standard_tools in Nova Sonic connect

Same pattern as the earlier get_setup_params fix: when context tools
are absent, the fallback `adapter.from_standard_tools(self._tools)`
can return the NotGiven sentinel, and `_send_prompt_start_event`
expects a list. Coerce via `or []` so the NotGiven case becomes an
empty list.

src/pipecat/services/aws/nova_sonic/llm.py

@@ -654,7 +654,7 @@ class AWSNovaSonicLLMService(LLMService):
         tools = (
             llm_connection_params["tools"]
             if llm_connection_params["tools"]
-            else adapter.from_standard_tools(self._tools)
+            else (adapter.from_standard_tools(self._tools) or [])
         )
         logger.debug(f"Using tools: {tools}")
         await self._send_prompt_start_event(tools)