Fixed missing null check on app template attribute of loader script.
Fixed missing null check on app template attribute of loader script.

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