OpenSSL: Reject empty cipher list in tls_connection_set_cipher_list()

Previously, this invalid call would have resulted in printing out a
string from uninitialized memory

Signed-off-by: Jouni Malinen <j@w1.fi>

src/crypto/tls_openssl.c

@@ -4437,6 +4437,10 @@ int tls_connection_set_cipher_list(void *tls_ctx, struct tls_connection *conn,
 
 		c++;
 	}
+	if (!buf[0]) {
+		wpa_printf(MSG_DEBUG, "OpenSSL: No ciphers listed");
+		return -1;
+	}
 
 	wpa_printf(MSG_DEBUG, "OpenSSL: cipher suites: %s", buf + 1);