BUG/MINOR: ssl: revert empty handshake detection in OpenSSL <= 1.0.2

BUG/MINOR: ssl: revert empty handshake detection in OpenSSL <= 1.0.2

Commit 54832b97 ("BUILD: enable several LibreSSL hacks, including")
changed empty handshake detection in OpenSSL <= 1.0.2 and LibreSSL,
from accessing packet_length directly (not available in LibreSSL) to
calling SSL_state() instead.

However, SSL_state() appears to be fully broken in both OpenSSL and
LibreSSL.

Since there is no possibility in LibreSSL to detect an empty handshake,
let's not try (like BoringSSL) and restore this functionality for
OpenSSL 1.0.2 and older, by reverting to the previous behavior.

Should be backported to 2.0.