crash pressing 'p' key if Picker is null
This issue was created automatically from an original Mantis Issue. Further discussion may take place here.
Playing with vtk, I found that my app was crashing if i pressed the 'p' key (to pick at the current mouse location). I debugged and the problem is that null is being dereferenced.
I have fixed the bug (cleanly & simply I believe) and am providing the patch in this bug. Please review it. thanks!