Fix #282: '/bin/ash': Permission denied
Created by: ollieparanoid
This was a regression from the improved input validation PR, which created the chroot_native folder with the wrong permissions (to test if we have write access to the work folder).
sjamaan found out, that this was the cause of the issue, and also explained how to fix it, thanks a lot!
@MartijnBraam: please merge after reviewing, thanks!