fix: answer returned null when response_mode was blocking (#1133)

api/services/completion_service.py

                         result = json.loads(result)
                         if result.get('error'):
                             cls.handle_error(result)
-                        if 'data' in result:
+                        if result['event'] == 'message' and 'data' in result:
                             return cls.get_message_response_data(result.get('data'))
             except ValueError as e:
                 if e.args[0] != "I/O operation on closed file.":  # ignore this error