vtkDecimatePolyline: Early return if the strategy's parameters are not valid
Fixes a bad behavior that allow the filter to run even if the selected strategy was not initialized properly. This fixes a bug with vtkCustomFieldStrategy
which could be run in its default state, with no source point array set.
paraview/paraview!6884 (merged) fixes another aspect of the problem, but the MRs are independant
Edited by Léon Victor