If we are unable to determine the Sending or Receiving endpoints, then not adding to the Knownendpoints list

- Fixes #279 
- Also relates to #277 

**NOTE:** I created this PR against the release-1.0.0 branch. Is that ok or should I be creating PR only against develop?
If so, I'll close this PR and re-create one agains the develop branch. 

@SimonCropp @johnsimons - code review?