Fix Autonav populateParentIDArray()

Fix `Autonav::populateParentIDArray()` to include '0'

- Autonav code was changed to remove check against non-existant variable
  `$stopAt`
- Previous code was passing string '0' in a check against `$stopAt`
  being `null`. Since this is PHP and the string '0' != null '0' zero
  was no longer added to the array.
- Now just check for > -1 since that check actually thinks the string
  '0' is the number 0
Merge pull request #1229 from mkly/fix_autonav_populate_parent_id_array

Fix Autonav populateParentIDArray()