Fixed crash under oSX after selection with SHIFT from 3DScene
Fixed crash under oSX after selection with SHIFT from 3DScene

prusa3d/Slic3r,prusa3d/Slic3r,prusa3d/Slic3r,prusa3d/Slic3r,prusa3d/Slic3r,prusa3d/Slic3r,prusa3d/Slic3r