BUG: Don't attempt to paint an empty plot.
BUG: Don't attempt to paint an empty plot.

If a plot has no points, then abort early.

Change-Id: Ia486aad8e3b42f44ae53ef48bc9c0252f7fce99a

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