vtkDataSet: Fix GetCellNumberOfFaces for VTK_CONVEX_POINT_SET
VTK_CONVEX_POINT_SET has dynamic size of faces, so the cell should be extracted to determine the number of faces.
This MR resolves paraview/paraview#22546 (closed).
Backport: release Backport: paraview/release
Edited by Spiros Tsalikis