Fix empty NewSessionTicket processing

Rebasing the state machine code introduced a problem with empty
NewSessionTicket processing. The return value from the
tls_process_new_session_ticket() is supposed to be an enum, but a bare
integer was being used. Unfortunately this is valid C so the compiler
doesn't pick it up.

Reviewed-by: Tim Hudson <tjh@openssl.org>
Reviewed-by: Richard Levitte <levitte@openssl.org>