Fix EXTMS error introduced by commit 94ed2c6

Commit 94ed2c6 dropped a ! operator by mistake, which causes extended
master secret connections to fail. This puts in back.

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

ssl/t1_enc.c

diff --git a/ssl/t1_enc.c b/ssl/t1_enc.c
index 37cd25d..d97b9a8 100644
--- a/ssl/t1_enc.c
+++ b/ssl/t1_enc.c
@@ -480,7 +480,7 @@
      * handshake hash). This will need to be removed later
      */
     if ((s->session->flags & SSL_SESS_FLAG_EXTMS)
-            && SSL_IS_TLS13(s)) {
+            && !SSL_IS_TLS13(s)) {
         unsigned char hash[EVP_MAX_MD_SIZE * 2];
         size_t hashlen;
         /*