Fixed a width of an empty icon, which added to BitmapComboBox
Fixed a width of an empty icon, which added to BitmapComboBox

Related to the #3759

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