index: don't include nullid in boundary check in pure code
Yet another change that should probably have been part of
a3dacabd476b
(index: don't allow index[len(index)] to mean nullid, 2018-07-20).
Differential Revision: https://phab.mercurial-scm.org/D4333
#require serve
$ hg clone http://localhost:$HGPORT/ copy
abort: * (glob)
[255]
$ test -d copy
[1]
$ $PYTHON "$TESTDIR/dumbhttp.py" -p $HGPORT --pid dumb.pid
$ cat dumb.pid >> $DAEMON_PIDS
$ hg clone http://localhost:$HGPORT/foo copy2
abort: HTTP Error 404: * (glob)
[255]
$ killdaemons.py