Fix handling of failed pixel formats
Fix handling of failed pixel formats

Added code to handle when a Stereo window can not
be obtained. fixed the code to check for failing
to get a pixel format.

SimVascular/VTK,keithroe/vtkoptix,sumedhasingla/VTK,SimVascular/VTK,sumedhasingla/VTK,keithroe/vtkoptix,SimVascular/VTK,SimVascular/VTK,keithroe/vtkoptix,sumedhasingla/VTK,sumedhasingla/VTK,sumedhasingla/VTK,SimVascular/VTK,sumedhasingla/VTK,keithroe/vtkoptix,SimVascular/VTK,keithroe/vtkoptix,keithroe/vtkoptix,sumedhasingla/VTK,keithroe/vtkoptix,SimVascular/VTK,SimVascular/VTK,keithroe/vtkoptix,sumedhasingla/VTK