The result of a read operation is a signed size_t, and cannot be
negative (except on error). Thus reading more than SSIZE_MAX bytes at
once is not well defined.

(Note: POSIX marks it as implementation-defined, and we cannot rely on
 much given the different implementations.)

In practice, this is not really a limitation for regular reads as
allocating a contiguous output buffer of more than SSIZE_MAX bytes is
essentially impossible. It can however be a problem when skipping data
(buffer pointer is NULL), especially on 32-bits platforms.

To skip such large amount of data, seeking is recommended instead,
e.g.:

    vlc_stream_Seek(s, vlc_stream_Tell() + skip);

instead of:

    vlc_stream_Read(s, NULL, skip);