Fix unintended utf8.reverse argument

[meehl]

utf8.gsub returns both the substituted string and the number of substitutions. Since the gsub calls are passed directly to utf8.reverse, both return values get forwarded, so the substitution count ends up as the second argument which is then interpreted as the optional lax argument.

This wraps the gsub calls in parentheses so only the substituted string is passed to utf8.reverse.

[meehl]

This fix also needs to be applied to PoB1.