Fix macro-spanning if in ssl_msg.c

Signed-off-by: David Horstmann <david.horstmann@arm.com>
diff --git a/library/ssl_msg.c b/library/ssl_msg.c
index e8f47de..815af7b 100644
--- a/library/ssl_msg.c
+++ b/library/ssl_msg.c
@@ -435,9 +435,12 @@
 
     unsigned char *cur = add_data;
 
+    int is_tls13 = 0;
 #if defined(MBEDTLS_SSL_PROTO_TLS1_3_EXPERIMENTAL)
-    if( minor_ver != MBEDTLS_SSL_MINOR_VERSION_4 )
+    if( minor_ver == MBEDTLS_SSL_MINOR_VERSION_4 )
+        is_tls13 = 1;
 #endif /* MBEDTLS_SSL_PROTO_TLS1_3_EXPERIMENTAL */
+    if( !is_tls13 )
     {
         ((void) minor_ver);
         memcpy( cur, rec->ctr, sizeof( rec->ctr ) );