Two logic errors caused valgrind to report "Conditional jump or move
depends on uninitialised value(s)" for TestReebGraph.

In vtkReebGraphSurfaceSkeletonFilter::RequestData()
also vtkReebGraphVolumeSkeletonFilter::RequestData()
1) Storing the wrong point id in meshToSubMeshmap. This resulted in
   bad vertexIds in the subMesh.
2) The logic for the contourFilter setup was
   incorrect. contourFilter->SetNumberOfContours(1); but
   contourFilter->SetValue(i, ...)

Please note with and without the changes the test passed.

Change-Id: I1ec4469fa6696616715ffc494ee756eaae1fd56a