libnm-core: empty key is not a pkcs12 file

nmcli> set 802-1x.ca-cert file:///tmp/certs/eaptest_ca_cert.pem
  (process:31015): libnm-CRITICAL **: crypto_is_pkcs12_data: assertion 'data != NULL' failed
  Error: failed to set 'ca-cert' property: PEM certificate had no start tag '-----BEGIN CERTIFICATE-----'.

libnm-core/crypto.c

@@ -641,6 +641,9 @@ crypto_is_pkcs12_data (const guint8 *data,
 	GError *local = NULL;
 	gboolean success;
 
+	if (!data_len)
+		return FALSE;
+
 	g_return_val_if_fail (data != NULL, FALSE);
 
 	if (!crypto_init (error))

libnm-util/crypto.c

@@ -654,6 +654,9 @@ crypto_is_pkcs12_data (const GByteArray *data)
 
 	g_return_val_if_fail (data != NULL, FALSE);
 
+	if (!data->len)
+		return FALSE;
+
 	success = crypto_verify_pkcs12 (data, NULL, &error);
 	if (success == FALSE) {
 		/* If the error was just a decryption error, then it's pkcs#12 */