UI_OpenSSL()'s session opener fails on MacOS X

If on a non-tty stdin, TTY_get() will fail with errno == ENODEV.
We didn't catch that.

Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/2039)
(cherry picked from commit c901bcce)