OWNxFromDistances: Fix crash when no edges and inverse is checked

[janezd]

Fixes #107.

[codecov-io]

Codecov Report

Merging #117 into master will not change coverage.
The diff coverage is 0%.

@@           Coverage Diff           @@
##           master     #117   +/-   ##
=======================================
  Coverage   62.14%   62.14%           
=======================================
  Files          29       29           
  Lines        2800     2800           
=======================================
  Hits         1740     1740           
  Misses       1060     1060

Impacted Files	Coverage Δ
orangecontrib/network/widgets/OWNxFromDistances.py	25.29% <0%> (ø)	⬆️

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