Another error occurs if donut chart.destroy() is called ~100ms after chart.unload()

[slaweet]

Description

@netil thank you very much for a quick fixing of #3614.

Another error occurs in the same scenario if I decrease the timeout from 500ms to 100ms.

Steps to check or reproduce

I've updated the timeout in the reproduction with nightly build of billboard: https://codesandbox.io/p/sandbox/billboard-error-after-destroy-forked-pw4xyq
it throws

TypeError
_$el is null
redraw
https://pw4xyq.csb.app/node_modules/billboard.js/dist/billboard.pkgd.js:31562:14
unload/<
https://pw4xyq.csb.app/node_modules/billboard.js/dist/billboard.pkgd.js:38571:10
end
https://pw4xyq.csb.app/node_modules/billboard.js/dist/billboard.pkgd.js:23668:21
call
https://pw4xyq.csb.app/node_modules/billboard.js/dist/billboard.pkgd.js:21136:72
tick
https://pw4xyq.csb.app/node_modules/billboard.js/dist/billboard.pkgd.js:22093:15
timerFlush
https://pw4xyq.csb.app/node_modules/billboard.js/dist/billboard.pkgd.js:21900:48
wake
https://pw4xyq.csb.app/node_modules/billboard.js/dist/billboard.pkgd.js:21909:5

[netil]

@slaweet, thanks again.
Basically, we recommend use in defensive approach. Usually calling other task which previous task haven't finished, eventually will make unexpected error.

For example, when calling some async load call, call next command when load task is done using load's done option.
Aside of comment, I'll look for preventing this.