Fixed crashing when moving VTK cell across sheet
Fixed crashing when moving VTK cell across sheet

hjanime/VisTrails,celiafish/VisTrails,celiafish/VisTrails,hjanime/VisTrails,Nikea/VisTrails,Nikea/VisTrails,minesense/VisTrails,VisTrails/VisTrails,hjanime/VisTrails,VisTrails/VisTrails,hjanime/VisTrails,celiafish/VisTrails,celiafish/VisTrails,VisTrails/VisTrails,hjanime/VisTrails,Nikea/VisTrails,Nikea/VisTrails,VisTrails/VisTrails,minesense/VisTrails,minesense/VisTrails,minesense/VisTrails,VisTrails/VisTrails,minesense/VisTrails