digital_ocean #3438: use get instead of [] to prevent KeyError

The existing code was using:
  a[b][c[d]]
where a[b] would always exist and c[d] would always exist.
But the nested index would not alway exist, particularly when a DigitalOcean item disapeared.

This changes that nested index to a `get` and properly handles None results.

This bug was present in two spots in this file.
Merge pull request #3806 from neomantra/issue_3438_x

digital_ocean #3438: use get instead of [] to prevent KeyError