BUG:8554. Try to fix headless Mac better (don't call subsequent gl functions if there is no OpenGL context).
BUG:8554. Try to fix headless Mac better (don't call subsequent gl functions if there is no OpenGL context).

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