Fixed validation the buffer size option

[dmitry-sles-novikov]

No description provided.

[upa]

plz describe the change.

[dmitry-sles-novikov]

You double-check o->buf_sz for 0, but you don't check for a negative value:

if (o->buf_sz == 0)
...
else if (o->buf_sz == 0) 

This options used to allocate a buffer and it would be good idea to check it for negative values =)

static int copy_chunk_r2l(struct chunk *c, sftp_file sf, int fd, int nr_ahead, int buf_sz, struct bwlimit *bw, size_t *counter)
{
    ....
    char buf[buf_sz];