tls13: Send dummy CCS only once

Fix cases where the client was sending
two CCS, no harm but better to send only one.

Prevent to send even more CCS when early data
are involved without having to add conditional
state transitions.

Signed-off-by: Ronald Cron <ronald.cron@arm.com>

library/ssl_tls13_generic.c

@@ -1390,6 +1390,8 @@ int mbedtls_ssl_tls13_write_change_cipher_spec(mbedtls_ssl_context *ssl)
     /* Dispatch message */
     MBEDTLS_SSL_PROC_CHK(mbedtls_ssl_write_record(ssl, 0));
 
+    ssl->handshake->ccs_count++;
+
 cleanup:
 
     MBEDTLS_SSL_DEBUG_MSG(2, ("<= write change cipher spec"));