Fixed logic to work when an empty vtkSelection is passed.
Fixed logic to work when an empty vtkSelection is passed.

vtkChartXY didn't update the selection if an empty vtkSelection was
passed. It should have cleared the selection, since it's now being set
to 'empty'. Fixed that.

This fixes the issue in ParaView where is the selection wasn't cleared
when expected (BUG #14935).

Change-Id: I947b13c2b5885c4e182c35013f1fe491d6839c56

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