STYLE: Set pointers to NULL, instead of 0, in vtkPlotBar
STYLE: Set pointers to NULL, instead of 0, in vtkPlotBar

This is consistant with usage in vtkPlot and vtkPlotPoints.

NULL is a memory location, 0 is an integer value.

Change-Id: I35c8b03e1a7ed137d7425c6db77e937cddc5f2c8

hendradarwin/VTK,berendkleinhaneveld/VTK,johnkit/vtk-dev,hendradarwin/VTK,keithroe/vtkoptix,johnkit/vtk-dev,msmolens/VTK,keithroe/vtkoptix,demarle/VTK,collects/VTK,aashish24/VTK-old,SimVascular/VTK,msmolens/VTK,cjh1/VTK,msmolens/VTK,biddisco/VTK,daviddoria/PointGraphsPhase1,gram526/VTK,berendkleinhaneveld/VTK,demarle/VTK,jmerkow/VTK,jmerkow/VTK,johnkit/vtk-dev,sankhesh/VTK,gram526/VTK,biddisco/VTK,sankhesh/VTK,SimVascular/VTK,cjh1/VTK,msmolens/VTK,SimVascular/VTK,ashray/VTK-EVM,candy7393/VTK,biddisco/VTK,hendradarwin/VTK,candy7393/VTK,keithroe/vtkoptix,SimVascular/VTK,msmolens/VTK,mspark93/VTK,spthaolt/VTK,hendradarwin/VTK,sankhesh/VTK,candy7393/VTK,berendkleinhaneveld/VTK,keithroe/vtkoptix,ashray/VTK-EVM,demarle/VTK,johnkit/vtk-dev,sankhesh/VTK,daviddoria/PointGraphsPhase1,sumedhasingla/VTK,jmerkow/VTK,sumedhasingla/VTK,mspark93/VTK,demarle/VTK,hendradarwin/VTK,aashish24/VTK-old,sumedhasingla/VTK,demarle/VTK,cjh1/VTK,SimVascular/VTK,jmerkow/VTK,SimVascular/VTK,biddisco/VTK,keithroe/vtkoptix,spthaolt/VTK,msmolens/VTK,sankhesh/VTK,candy7393/VTK,mspark93/VTK,mspark93/VTK,hendradarwin/VTK,candy7393/VTK,ashray/VTK-EVM,jmerkow/VTK,biddisco/VTK,spthaolt/VTK,mspark93/VTK,gram526/VTK,sankhesh/VTK,berendkleinhaneveld/VTK,jmerkow/VTK,mspark93/VTK,spthaolt/VTK,biddisco/VTK,sumedhasingla/VTK,daviddoria/PointGraphsPhase1,spthaolt/VTK,berendkleinhaneveld/VTK,msmolens/VTK,demarle/VTK,sankhesh/VTK,cjh1/VTK,keithroe/vtkoptix,daviddoria/PointGraphsPhase1,daviddoria/PointGraphsPhase1,berendkleinhaneveld/VTK,daviddoria/PointGraphsPhase1,jmerkow/VTK,sumedhasingla/VTK,mspark93/VTK,keithroe/vtkoptix,gram526/VTK,candy7393/VTK,SimVascular/VTK,gram526/VTK,gram526/VTK,johnkit/vtk-dev,collects/VTK,hendradarwin/VTK,ashray/VTK-EVM,collects/VTK,aashish24/VTK-old,spthaolt/VTK,demarle/VTK,mspark93/VTK,sankhesh/VTK,ashray/VTK-EVM,candy7393/VTK,sumedhasingla/VTK,jmerkow/VTK,aashish24/VTK-old,biddisco/VTK,SimVascular/VTK,aashish24/VTK-old,demarle/VTK,ashray/VTK-EVM,sumedhasingla/VTK,collects/VTK,cjh1/VTK,collects/VTK,cjh1/VTK,candy7393/VTK,gram526/VTK,ashray/VTK-EVM,johnkit/vtk-dev,johnkit/vtk-dev,keithroe/vtkoptix,collects/VTK,aashish24/VTK-old,sumedhasingla/VTK,spthaolt/VTK,ashray/VTK-EVM,berendkleinhaneveld/VTK,gram526/VTK,msmolens/VTK