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: NTim Hudson <tjh@openssl.org>
Reviewed-by: NRichard Levitte <levitte@openssl.org>

ssl/statem/statem_clnt.c

@@ -2184,7 +2184,7 @@ enum MSG_PROCESS_RETURN tls_process_new_session_ticket(SSL *s, PACKET *pkt)
 
     /* Server is allowed to change its mind and send an empty ticket. */
     if (ticklen == 0)
-        return 1;
+        return MSG_PROCESS_CONTINUE_READING;
 
     if (s->session->session_id_length > 0) {
         int i = s->session_ctx->session_cache_mode;