BUG: Must check after we have a valid context.
BUG: Must check after we have a valid context.

This can cause segfaults on some mesa.

Change-Id: I6c4f8d0ce8111cadbf685cff8c66e6bcfb29995d

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