StringUtils::Tokenize: clarify, simplify and optimize

Variables names were wrong, no need to check "pos" for "string::npos", comments were incorrect (notice `// Find first "non-delimiter"`).
@jmarshallnz ?
That what I thought at first. :)
But notice '||' in while condition. :)
`lastPos` can be not `npos` when `pos` is `npos` but not vice versa. So check of `pos` is not required.