str: use strnlen to determine string length
str: use strnlen to determine string length

This serves two purposes:

(1) we determine the length of strings that we didn't get a length for
(2) we sanity check that the non-nul-terminated strings don't contain nuls

Signed-off-by: Josef 'Jeff' Sipek <a620f141433c70aa9e43778305a6c68cbfadfb25@josefsipek.net>

jeffpc/libjeffpc,jeffpc/libjeffpc,jeffpc/libjeffpc,jeffpc/libjeffpc