Clarify "negotiating"

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/include/mbedtls/ssl.h b/include/mbedtls/ssl.h
index 2739331..466c734 100644
--- a/include/mbedtls/ssl.h
+++ b/include/mbedtls/ssl.h
@@ -4927,7 +4927,9 @@
  *                 subsystem must have been initialized by calling
  *                 psa_crypto_init() before calling this function.
  *                 Otherwise, the handshake may call psa_crypto_init()
- *                 if it ends up negotiating TLS 1.3.
+ *                 if a negotiation involving TLS 1.3 takes place (this may
+ *                 be the case even if TLS 1.3 is offered but eventually
+ *                 not selected).
  */
 int mbedtls_ssl_handshake(mbedtls_ssl_context *ssl);