Fix runtime critical when message is cancelled after a failed auth
When the message is restarted due to the failed auth, we fail to properly reset the SoupSession:ostream data on the item task and we end up calling async_send_request_return_result() twice causing the following critical the second time:
(auth-test:66750): libsoup-CRITICAL **: 15:48:08.156: async_send_request_return_result: assertion 'item->task != NULL' failed
SoupSession:ostream data is set in item task, but we reset in item message.