wc: should report correct count on multibyte input

[xtqqczze]

wc/wc.pl: wc -c -m on multibyte input reports the wrong count

[darkraider01]

Hey, I'd like to take a look at this one.

I traced the -c -m path a bit and it seems to go through the fast character counting code in count_fast.rs, so I want to first reproduce the exact wc.pl failure and check how it's behaving with invalid/multibyte input.

I'll add a focused regression test once I pin down the case, then work from there. Is it okay if I take this?

[xtqqczze]

taken by @darkraider01