data-out: Make binary output buffer big enough for a null terminator.

data-out: Make binary output buffer big enough for a null terminator.

The max width for binary output is 16, for P or PK format, plus there
needs to be room for a null terminator, for a total width of 17 bytes.
The buffer here was undersized at only 16 bytes.  This commit fixes the
problem.

Thanks to Youngseok Choi for reporting the bug.