Ensure the WPACKET gets cleaned up in the event of an error

Otherwise a mem leak can occur.
Reviewed-by: NRich Salz <rsalz@openssl.org>

ssl/statem/statem_clnt.c

@@ -875,6 +875,7 @@ int tls_construct_client_hello(SSL *s)
     return 1;
  err:
     ossl_statem_set_error(s);
+    WPACKET_cleanup(&pkt);
     return 0;
 }