Don't color by texture in `IndexedLookup` mode.
Don't color by texture in `IndexedLookup` mode.

Using a texture map to color geometry assumes
that interpolation can be performed (although
this can be disabled with `GL_NEAREST`)  and
that scalar values are numeric. This need not
be true in indexed lookup mode as annotations
may be string- or variant-valued.

Change-Id: I4c0d29c57db48e9754ee2ac7d67defadc3a3a9de

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