Fix vtkOpenVRHardwarePicker -Wnarrowing warnings
/home/jcfr/Projects/Slicer-Qt5-VTK9-Release/VTKv9/Rendering/OpenVR/vtkOpenVRHardwarePicker.cxx: In member function ‘virtual int vtkOpenVRHardwarePicker::PickProp(double*, double*, vtkRenderer*, vtkPropCollection*)’:
/home/jcfr/Projects/Slicer-Qt5-VTK9-Release/VTKv9/Rendering/OpenVR/vtkOpenVRHardwarePicker.cxx:108:37: warning: narrowing conversion of ‘((* size) / 2)’ from ‘int’ to ‘unsigned int’ inside { } [-Wnarrowing]
unsigned int inPos[2] = {size[0]/2, size[1]/2};
^
/home/jcfr/Projects/Slicer-Qt5-VTK9-Release/VTKv9/Rendering/OpenVR/vtkOpenVRHardwarePicker.cxx:108:48: warning: narrowing conversion of ‘((*(size + 4u)) / 2)’ from ‘int’ to ‘unsigned int’ inside { } [-Wnarrowing]
unsigned int inPos[2] = {size[0]/2, size[1]/2};
^