Fix #740: Segmentation fault when "r" is pressed

Segmentation fault when "r" is pressed in PCLVisualizer.
The previous pull request #703 does not handle the "r" keyboard event
correctly and pass the event to vtkInteractorStyleRubberBandPick,
which enables rubber-band selection mode when 'r' is pressed.
Merge pull request #742 from xiangxw/fix_pclvisualizer_r_pressed

Fix #740 and #732: Segmentation fault when "r" is pressed