bug#7357: csplit: memory exhausted when using stdout / pipe instead of a file

[Paul Eggert]

> +  unsigned int max_digit_string_len
> +    = (suffix
> +       ? max_out (suffix)
> +       : MAX (INT_STRLEN_BOUND (unsigned int), digits));

That should be size_t, not unsigned int, since max_out
returns a size_t, and it could return a value greater than
UINT_MAX.  For example, the user might run "csplit -b %4294967296d"
and on a 64-bit host max_out will return UINTMAX + 1.

While we're on the subject of undefined printf behavior, perhaps
we should be rejecting any attempt to use a printf format like
%4294967296d that uses a width or precision greater than INT_MAX?
POSIX seems to say that such a format should work, but I'll bet
nobody does it right (glibc doesn't).  For safety we might want
to be truncating large widths or precisions to INT_MAX, or
rejecting them.