Showing it was only displaying the top modes, with a lot of top space,
and you had to slowly scroll down the list. This is the same as #2642
(as Alexandre noted in a comment), so I just use the same "fix" though I
don't fully understand it. It feels more of a side effect of
gtk_combo_box_set_wrap_width() working around a bug of GtkComboBox. So
if anyone has a better fix and understand the issue, feel free to patch
(maybe GTK+ directly?). In the meantime, it works well enough. :-)

(cherry picked from commit 6dfca83c)