Errors from SSL_write() not handled properly for TLS

When SSL_write() return <= 0 we don't handle that in any other way than calling ERR_get_error() until the error stack is empty. We print an error message but don't call SSL_write() again (SSL_ERROR_WANT_*) or close the connection (the rest of them).

In the DTLS case, the closing case is handled by clientradputdtls() returning a different value (0) and might not be an issue. I haven't looked closely at that.