[Bug] NoneType error when resending SMS before saving (resend before initial send)

[danielxue]

See https://penn-labs.sentry.io/issues/4221802209/?project=6171869&query=is%3Aunresolved&referrer=issue-stream&stream_index=0

We should decide if we should just not allow resend before initial send, have specific error message, or just do an initial send.