Cleanup some code around tls-unique binding in TLSv1.3
- The binding call should fail first of all, as tls-unique binding type is not defined under TLSv1.3. The test unit is updated accordingly.
- New GnuTLS backend is handling it properly but old returns success/empty data - handle empty data and return error.
- OpenSSL returns success (or rather Finished packet, as it is asked for) hence catch this condition before the call and return error.
Fixes #181 (closed) and #164 (closed)
Edited by Ruslan Marchenko