For a console readall(), if the first line starts with '\x1a' (i.e. Ctrl+Z), it breaks out of its read loop before incrementing len. Thus the input isn't handled properly as EOF, for which the check requires len > 0. Instead it ends up calling WideCharToMultiByte with len == 0, which fails as follows:

    >>> sys.stdin.buffer.raw.read()
    ^Z
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
    OSError: [WinError 87] The parameter is incorrect