fix logic for shuffling results (#3619)

@alexbarghi-nv found a bug in sampling during python testing.  The process of shuffling sampled edges for output formatting was corrupting the label associated with each sampled edge.  This PR fixes this bug.

Authors:
  - Chuck Hastings (https://github.com/ChuckHastings)

Approvers:
  - Seunghwa Kang (https://github.com/seunghwak)
  - Naim (https://github.com/naimnv)

URL: #3619