vktDataObjectTree: Fix CopyStructure bug
vktDataObjectTree: Fix CopyStructure bug

When the input to CopyStructure() is vtkDataObject, instead of just
bailing out, create a flat tree with same number of blocks as the
source.

This fixes a set of ParaView dashboard tests,
e.g. pvcs.CTHAMRBaseline, pvcs.TestIsoVolume, which all invoke the
function in vtkCompositeDataPipeline to compute multiblock poly data
over amr that contain null blocks.

Change-Id: Ia8696f10fba0d975009adde0419aa4506ef055a2

sumedhasingla/VTK,msmolens/VTK,sumedhasingla/VTK,demarle/VTK,sankhesh/VTK,biddisco/VTK,msmolens/VTK,aashish24/VTK-old,berendkleinhaneveld/VTK,hendradarwin/VTK,SimVascular/VTK,johnkit/vtk-dev,hendradarwin/VTK,keithroe/vtkoptix,jmerkow/VTK,sankhesh/VTK,mspark93/VTK,sumedhasingla/VTK,msmolens/VTK,ashray/VTK-EVM,candy7393/VTK,candy7393/VTK,mspark93/VTK,aashish24/VTK-old,demarle/VTK,SimVascular/VTK,aashish24/VTK-old,collects/VTK,berendkleinhaneveld/VTK,msmolens/VTK,mspark93/VTK,gram526/VTK,collects/VTK,aashish24/VTK-old,jmerkow/VTK,hendradarwin/VTK,ashray/VTK-EVM,SimVascular/VTK,keithroe/vtkoptix,sumedhasingla/VTK,gram526/VTK,gram526/VTK,johnkit/vtk-dev,sankhesh/VTK,collects/VTK,keithroe/vtkoptix,demarle/VTK,candy7393/VTK,biddisco/VTK,jmerkow/VTK,jmerkow/VTK,johnkit/vtk-dev,collects/VTK,candy7393/VTK,berendkleinhaneveld/VTK,mspark93/VTK,keithroe/vtkoptix,johnkit/vtk-dev,mspark93/VTK,sankhesh/VTK,mspark93/VTK,keithroe/vtkoptix,SimVascular/VTK,keithroe/vtkoptix,candy7393/VTK,sumedhasingla/VTK,candy7393/VTK,biddisco/VTK,msmolens/VTK,demarle/VTK,collects/VTK,ashray/VTK-EVM,hendradarwin/VTK,johnkit/vtk-dev,hendradarwin/VTK,jmerkow/VTK,aashish24/VTK-old,keithroe/vtkoptix,SimVascular/VTK,candy7393/VTK,biddisco/VTK,hendradarwin/VTK,sankhesh/VTK,johnkit/vtk-dev,johnkit/vtk-dev,mspark93/VTK,sankhesh/VTK,collects/VTK,demarle/VTK,sumedhasingla/VTK,demarle/VTK,berendkleinhaneveld/VTK,ashray/VTK-EVM,sumedhasingla/VTK,msmolens/VTK,gram526/VTK,ashray/VTK-EVM,berendkleinhaneveld/VTK,demarle/VTK,sumedhasingla/VTK,biddisco/VTK,gram526/VTK,gram526/VTK,sankhesh/VTK,gram526/VTK,hendradarwin/VTK,keithroe/vtkoptix,demarle/VTK,msmolens/VTK,biddisco/VTK,jmerkow/VTK,biddisco/VTK,jmerkow/VTK,berendkleinhaneveld/VTK,ashray/VTK-EVM,SimVascular/VTK,gram526/VTK,msmolens/VTK,ashray/VTK-EVM,candy7393/VTK,sankhesh/VTK,ashray/VTK-EVM,SimVascular/VTK,SimVascular/VTK,berendkleinhaneveld/VTK,aashish24/VTK-old,mspark93/VTK,jmerkow/VTK