Fog #1620

Guarding around a few possibilities of nil that I discovered while trying to mock up address association in a VPC.  The relevant issue is:

[#1620](https://github.com/fog/fog/issues/1620)

I'm not sure how valid the response will be after this. If this makes things worse, feel free to disregard.  I should probably fire up a test environment in AWS to gather enough test cases and response to further flush out this mock.