Thanks. It would perhaps be reasonable to test /var/www/html/index.* as well, perhaps, and skip the move if any of those exist, presuming that the user is already using /var/www/html. I can see this might fail if somebody is using a DocumentRoot of /var/www and simply has an html/ directory being served with further files in it.
This needs checking against Debian and a bug filed there if relevant. Whichever way Debian concludes is the best way to do this is what Ubuntu should do as well.