Fix signed/unsigned warning in HTG.
Fix signed/unsigned warning in HTG.

Change-Id: I25be3f3329ab9a228865c64caaf7dfea287fd049

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