Issue #13848: open() and the FileIO constructor now check for NUL characters in the file name.

Patch by Hynek Schlawack.

Objects/unicodeobject.c

@@ -1866,6 +1866,19 @@ PyUnicode_DecodeFSDefaultAndSize(const char *s, Py_ssize_t size)
 }
 
 
+int
+_PyUnicode_HasNULChars(PyObject* s)
+{
+    static PyObject *nul = NULL;
+
+    if (nul == NULL)
+        nul = PyUnicode_FromStringAndSize("\0", 1);
+    if (nul == NULL)
+        return -1;
+    return PyUnicode_Contains(s, nul);
+}
+
+
 int
 PyUnicode_FSConverter(PyObject* arg, void* addr)
 {