Fix of tripping glAssert after switching to Preview on Linux/GTK2 (fix suggested and thus approved by @enricoturri1966)
Fix of tripping glAssert after switching to Preview on Linux/GTK2
(fix suggested and thus approved by @enricoturri1966)

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