Fixed when testing the openai compatible interface model, an error is reported when no object is returned (#7808)

api/core/model_runtime/model_providers/openai_api_compatible/llm/llm.py

             except json.JSONDecodeError as e:
                 raise CredentialsValidateFailedError('Credentials validation failed: JSON decode error')
 
-            if (completion_type is LLMMode.CHAT and json_result['object'] == ''):
+            if (completion_type is LLMMode.CHAT and json_result.get('object','') == ''):
                 json_result['object'] = 'chat.completion'
-            elif (completion_type is LLMMode.COMPLETION and json_result['object'] == ''):
+            elif (completion_type is LLMMode.COMPLETION and json_result.get('object','') == ''):
                 json_result['object'] = 'text_completion'
 
             if (completion_type is LLMMode.CHAT