[Toybox] [PATCH] Fix segfault in sed -e 'c\'

[Andy Chu]

> I applied your segfault fix, but I think I'll wait for somebody to show
> something this part breaks?

Yeah it doesn't seem like something anyone should rely on, so I think
it makes to do the simple fix first.

> Thanks for the fix. Did your fuzzer find anything else?

Not yet...  The sed -f input was literally the first thing I tried and
that dropped out almost instantly.  I just tried fuzzing the grep
expression and chmod mode but it didn't find anything.

I have a patch to main.c to allow afl-fuzz to fuzz arbitrary params
(it works on a model of files, so sed -f was easy to fuzz, but other
things require instrumentation).  If it can find a few more bugs that
may be worth it.

BTW I didn't see the patch applied here?
https://github.com/landley/toybox/commits/master

thanks,
Andy

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