`_PyUnicode_TransformDecimalAndSpaceToASCII()` missed trailing NUL char.
It caused buffer overflow in `_Py_string_to_number_with_underscores()`.

This bug is introduced in 9b6c60cb.
(cherry picked from commit 16dfca4d)
Co-authored-by: INADA Naoki <methane@users.noreply.github.com>