SSL: restore handlers after blocking. It is possible that after SSL_read() will return SSL_ERROR_WANT_WRITE, further calls will return SSL_ERROR_WANT_READ without reading any application data. We have to call ngx_handle_write_event() and switch back to normal write handling much like we do if there are some application data, or the write there will be reported again and again. Similarly, we have to switch back to normal read handling if there is saved read handler and SSL_write() returns SSL_ERROR_WANT_WRITE.