[PATCH v5] libio: asprintf should write NULL upon failure

[Florian Weimer]

* Sam James:

>> v5: Repost to address Makefile conflict.
>
> Not that it was needed here, but I wonder if we should encourage people
> posting range-diffs. It would help me sometimes at least.

Maybe we can teach Patchwork to generate them for us.

Thanks,
Florian