don't segfault when \N escapes are used and unicodedata fails to load
Fixes #4367
diff --git a/Python/ast.c b/Python/ast.c
index 6eb3aa4..02aa2a7 100644
--- a/Python/ast.c
+++ b/Python/ast.c
@@ -1294,13 +1294,14 @@
if (PyErr_ExceptionMatches(PyExc_UnicodeError)){
PyObject *type, *value, *tback, *errstr;
PyErr_Fetch(&type, &value, &tback);
- errstr = ((PyUnicodeErrorObject *)value)->reason;
+ errstr = PyObject_Str(value);
if (errstr) {
char *s = "";
char buf[128];
s = PyString_AsString(errstr);
PyOS_snprintf(buf, sizeof(buf), "(unicode error) %s", s);
ast_error(n, buf);
+ Py_DECREF(errstr);
} else {
ast_error(n, "(unicode error) unknown error");
}