wpa_supplicant: Fix NULL dereference in tls_verify_cb()

In function tls_verify_cb(), X509_STORE_CTX_get_current_cert() may
return NULL, and it will be dereferenced by X509_get_subject_name().

Signed-hostap: Eytan Lifshitz <eytan.lifshitz@intel.com>

src/crypto/tls_openssl.c

@@ -1368,6 +1368,9 @@ static int tls_verify_cb(int preverify_ok, X509_STORE_CTX *x509_ctx)
 	const char *err_str;
 
 	err_cert = X509_STORE_CTX_get_current_cert(x509_ctx);
+	if (!err_cert)
+		return 0;
+
 	err = X509_STORE_CTX_get_error(x509_ctx);
 	depth = X509_STORE_CTX_get_error_depth(x509_ctx);
 	ssl = X509_STORE_CTX_get_ex_data(x509_ctx,