wc: fix out-of-bounds read for single-byte wide characters

wc: fix out-of-bounds read for single-byte wide characters

In legacy CJK locales a single input byte can decode to a wide character
above UCHAR_MAX, e.g. SHIFT-JIS bytes 0xA1..0xDF become U+FF61..U+FF9F.
wc then indexed its 256-entry wc_isprint/wc_isspace tables with that
value and read past their end.
* src/wc.c (wc): Take the byte-indexed fast path only when the decoded
character fits in a byte; wider values fall through to c32width and
c32isspace.
* tests/wc/wc-sjis.sh: New test.
* tests/local.mk (all_tests): Add it.
* NEWS: Mention the fix.

Link: https://github.com/coreutils/coreutils/pull/298