Heatmap crash when no checks are available for the request

Sentry Issue: WAVEQC-13

IndexError: too many indices for array: array is 1-dimensional, but 3 were indexed
(11 additional frame(s) were not displayed)
...
  File "waveqc/views.py", line 357, in network_detail
    return self.context(query, label, pk, items)
  File "waveqc/views.py", line 234, in context
    figure = self.figure(
  File "waveqc/views.py", line 177, in figure
    z=results[:, :, 0] + results[:, :, 1],