Minor fix for clearing the zbuffer
Minor fix for clearing the zbuffer

Change-Id: If81c969da898c41bf6b0910739e73ed528b9ee9a

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