TLS code is not robust against SSL_ERROR_WANT_READ retry

Read operations on in SSL/TLS can return a retriable error `SSL_ERROR_WANT_READ` in which case the read operation should be repeated. The current implementation will fail with `rsc_abort` and treat it as read error, which it shouldn't.

Currently, it's possible to reproduce using `RS.authkey()` on a TLS connection since it takes some time for the server to generate a key.