Comment 7 for bug 2063899

So, I overlooked this earlier:

    # There has got to be a better way to do this.
    if [ "$(grep -Fx 'EXTRA_GROUPS="audio' /etc/adduser.conf)" = "" ]; then
        echo -e "\n# Ubuntu Studio Configuration\n# Add other EXTRA_GROUPS before this line" >> /etc/adduser.conf
        echo 'EXTRA_GROUPS="audio"' >> /etc/adduser.conf
    fi
    if [ "$(grep -Fx 'ADD_EXTRA_GROUPS=1' /etc/adduser.conf)" = "" ]; then
            echo 'ADD_EXTRA_GROUPS=1' >> /etc/adduser.conf
    fi

/etc/adduser.conf is a conffile owned by the adduser package. Modifying it from package maintainer scripts is not allowed.