debian/src/sysv-rc/sbin/invoke-rc.d: tweak behavior of invoke-rc.d when a package has an upstart job without a corresponding init script, and we're running on a non-upstart system, *butpolicy-rc.d says to not take the action. In this case, we want to exit zero instead of non-zero, as this is an important use case when setting up Ubuntu in a chroot.