Bugfix for bottleneck in vtkGraph::RemoveVertexInternal

Originally contributed by Matthias Schneider. This was an oversight
where other calls to BuildEdgeList are guarded by this condition.

Change-Id: I0a43e062c50636b45c5f71821ab01a7d68c72d50
Merge topic 'vtkgraph-vertex-remove-bottleneck' into master

566bef8d Bugfix for bottleneck in vtkGraph::RemoveVertexInternal