I started bisect at commit f5c110199675b7f4c50d4a7a64b6aac44c55d0a4, where it
kind of works, i.e. does not crash, but the widgets start to appear only after
redraw (mouse hover or slider moved).

And this is the culprit which makes it segfault (i.e. from kind of working as
above to not working and then it was "fixed" where it does not segfault but
does not redraw either).

6b284f08ab399154ad10e2166440b44cbbdcb2c5