response_data not initialized

With the recent version I triggered cases where response_data was not initialized. I can't provide any more details due to limited access to my systems right now.

https://gitlab.com/stavros/pysignald/-/blob/0156bd863989fbedbc2b292e6dd4002da81b6065/signald/main.py#L82

Maybe next week I'll be able to isolate the cases (or provide a fix).

/cc @eranrund